THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


PNEUMATICS. 


A  GLANCE  AT  THE  SCIENCES. 


BOSTON: 
G.    C.    RAND  — WM.    J.    REYNOLDS    &    CO. 


GLANCE 

AT    THE 

PHYSICAL    SCIENCES; 

OR    THE 

WONDERS   OF  NATURE, 

IN 

EARTH,  AIR,  AND  SKY: 


BY    THE    AUTEOR    OF 


PETER    PARLEY'S    TALES. 


BOSTON: 

PUBLISHED    BY    GEO.    C.   HAND,    CORXHILL. 

WM.  J.  REYNOLDS   AND   COMPANY. 

1852. 


PRESS   OF  GEORGE   C.   RA>"D  &   C"" 


QI63 


CONTENTS 

PAGE. 

ASTRONOMY, 9 

The  Solar  System, 12 

The  Planet  Mercury, 16 

The  Planet  Venus, 17 

The  Earth, 17 

The  Planet  Mars, 25 

Ceres,  Pallas,  Juno,  and  Vesta 26 

The  Planet  Jupiter, 27 

The  Planet  Saturn, 28 

The  Planet  Uranus, 32 

General  Remarks  on  the  Planets,    .        .     '   .        .  32 

Comets, .36 

The  Fixed  Stars, *'.*      .  & 

Meteorites,        .        ...        .        .        .        .  48 

Aerolites,          .                          IP 

Nebulous  Stars,        .        .        .        ...        .        .  51 

The  Firmamental  Systems, 59 

PROPERTIES  OF  MATTER, 71 

THE  MECHANICAL  POWERS,. 85 

HYDROSTATICS,        .        .        .        .        .        .        .        .  99 

HYDRAULICS,  .        .        .        .        .        .        .        .109 

PNEUMATICS;   OR,  THE    MECHANICAL   PROPERTIES   OF 

AIR, 120 

OPTICS, .133 


4  CONTENTS. 

PAGE. 

ACOUSTICS, "•...,.  147 

ELECTRICITY, 158 

GALVANISM, 172 

MAGNETISM,    .   '     .        .        .        .       ,.        .        .        .182 

ELECTRO-MAGNETISM, 192 

MATHEMATICS, 195 

METEOROLOGY, 210 

CHEMISTRY, .  247 

GEOLOGY,        ..........  266 

Nature  of  the  Crust  of  the  Earth,    ....  268 

Classification  of  Rocks, 269 

Arrangement  of  Strata,    .:....  273 

Age  of  Rocks, 274 

Formation  of  Rocks  and  Strata,       .  275 

Fossil  Remains, 2S1 

Changes  of  the  Earth's  Surface,       .        .        .        .282 

Miscellaneous  Topics, 286 

MINERAL  KINGDOM, 289 

BOTANY, 302 

ZOOLOGY.        .                                .  339 


A  GIAXCE  AT  THE  SCIENCES. 


INTRODUCTION. 

NATUKAL  or  PHYSICAL  SCIENCE  is  as  boundless  in 
its  scope  as  die  extent  of  the  universe.  It  does  not 
confine  its  researches  to  the  narrow  circle  within  our 
own  observation :  it  is  not  content  with  the  investiga- 
tion of  objects  presented  to  the  naked  eye  :  it  goes  with 
the  telescope  into  the  heavens,  and  descends  with  the 
microscope  into  the  atom — every  where  discovering 
materials  for  its  consideration.  Nor  is  it  absorbed  with 
observations  upon  the  forms  and  hues  of  material  ob- 
jects :  it  seeks  out  the  hidden  laws  of  the  universe,  the 
principles  by  which  the  Architect  of  the  earth  and 
heavens  constructs  and  governs  his  boundless  do- 
minions. 

We  are  apt  to  wrap  up  the  true  idea  of  scientific 
investigations  in  a  bald  and  chilling  phraseology :  we 
call  them  studies  of  nature  ;  but  they  are,  in  tram, 
studies  into  the  ways  of  God.  What  is  natvrt,  sep- 
arate from  that  active  and  intelligent  Being  to  whom 
1* 


6  INTRODUCTION. 

we  are  indebted  for  life  and  light,  —  that  Being  who 
gave  us  the  Bible  as  well  as  the  Sun,  and  is  as  truly 
the  moral  as  he  is  the  natural  Governor  of  the  universe  ? 

The  true  mode  of  pursuing  scientific  studies  is  to 
regard  them  as  investigations  into  the  works  of  the 
Almighty,  and  every  where,  as  well  in  the  contem- 
plation of  the  starry  firmament  as  in  scrutinizing  the 
more  familiar  objects  of  our  own  globe,  to  realize  the 
presence  of  the  Creator.  In  this  way,  science  unseals 
the  volume  of  Nature's  revelation,  to  the  most  noble 
and  exalting  purposes. 

"  While  the  telescope,"  says  Dr.  Chalmers,  "  enables 
us  to  see  a  system  in  every  star,  the  microscope  un- 
folds to  us  a  world  in  every  atom.  The  one  instructs 
us  that  this  mighty  globe,  with  the  whole  burden  of  its 
people  and  its  countries,  is  but  a  grain  of  sand  in  the 
vast  field  of  immensity :  the  other,  that  every  atom 
may  harbor  the  tribes  and  families  of  a  busy  popula- 
tion. The  one  shows  us  the  insignificance  of  the 
world  we  inhabit :  the  other  redeems  it  from  all  its  in- 
significance ;  for  it  tells  us  that,  in  the  leaves  of  every 
forest,  in  the  flowers  of  every  garden,  in  the  waters  of 
every  rivulet,  there  are  worlds  teeming  with  life,  and 
numberless  as  are  the  stars  of  the  firmament.  The  one 
suggests  to  us  that,  above  and  beyond  all  that  is  visible 
to  man,  there  may  be  regions  of  creation  which  sweep 
immeasurably  along,  and  carry  the  impress  of  the  Al- 
mighty's hand  to  tbo  remotest  scenes  of  the  universe  •, 


INTRODUCTION.  7 

the  other  that,  within  and  beneath  all  that  minute- 
ness which  the  aided  eye  of  man  has  been  able  to 
explore,  there  may  be  a  world  of  invisible  beings ;  and 
that,  could  we  draw  aside  the  mysterious  curtain  which 
shrouds  it  from  our  senses,  we  might  behold  a  theatre 
of  as  many  wonders  as  astronomy  can  unfold  ;  a  uni- 
verse within  the  compass  of  a  point,  so  small  as  to 
elude  all  the  powers  of  the  microscope,  but  where  the 
Almighty  Ruler  of  all  things  finds  room  for  the  exer- 
cise of  His  attributes,  where  He  can  raise  another 
mechanism  of  worlds,  and  fill  and  animate  them  with 
all  the  evidence  of  His  glory." 

How  interesting,  how  instructive,  is  science,  while 
we  thus  walk  its  paths  in  the  light  of  God's  image,  and 
with  the  constant  assurance  that,  while  He  thus  pursues 
His  vast  operations,  He  is  still  presiding  over  the  beat- 
ing of  our  hearts,  and  that  not  even  the  sparrow  falls 
unnoticed  to  the  ground !  How  comparatively  barren 
and  desolate  are  the  works  of  creation,  if  the  Christian's 
God  is  every  where  invisible,  and  the  whole  phenom- 
ena of  nature  are  to  be  resolved  into  an  inscrutable 
series  of  causes  and  consequences  ! 

In  the  course  of  the  following  pages,  we  propose 
only  to  present  a  rapid  and  distinct  outline  of  Physical 
Science,  as  it  is  now  exhibited  in  the  works  of  learned 
men.  Within  the  present  century,  the  march  of 
knowledge  has  been  rapid  beyond  example,  and  at  the 
same  time,  the  most  wonderful  discoveries  have  been 


8  INTRODUCTION. 

brought  within  the  reach  of  every  reader.  Philosophy 
is  no  longer  sealed  up  in  learned  languages,  and  kept 
under  the  lock  and  key  of  colleges  and  universities. 
In  the  compass  of  this  little  volume,  we  hope  to  place 
within  the  reach  of  our  readers,  not  only  the  most  im- 
portant results  of  the  researches  of  Herschel  and 
Laplace  into  the  mechanism  of  the  heavens,  but  of 
those  of  Lyell,  Mantel,  and  others,  into  the  structure 
of  our  earth  ;  to  present  the  wonders  of  the  telescope 
and  the  microscope  ;  in  short,  to  open  the  book  of 
natural  philosophy,  and  take  a  glance  at  its  wonderfii 
revelations,  in  respect  to  the  stars  above,  and  the  ani 
mal,  vegetable,  and  mineral  kingdoms  here  below. 


ASTRONOMY. 


"  ASTRONOMY  is  that  department  of  knowledge  which 
has  for  its  object  to  investigate  the  motions,  the  magni 
tudes,  and  distances,  of  the  heavenly  bodies  ;  the  laws 
by  which  their  movements  are  directed,  and  the  ends 
they  are  intended  to  subserve  in  the  fabric  of  the  uni 
verse.  This  is  a  science  which  has  in  all  ages  engaged 
the  attention  of  the  poet,  the  philosopher,  and  the 
divine,  and  been  the  subject  of  their  study  and  admi- 
ration. Kings  have  descended  from  their  thrones  to 
render  it  homage,  and  have  sometimes  enriched  it  with 
their  labors;  and  humble  shepherds,  while  watching 


10  ASTRONOMY. 

their  flocks  by  night,  have  beheld  with  rapture  the  blue 
vault  of  heaven,  with  its  thousand  shining  orbs,  moving 
in  silent  grandeur,  till  the  morning  star  announced  the 
approach  of  day.  The  study  of  this  science  must  have 
been  coeval  with  the  existence  of  man  ;  for  there  is  nc 
rational  being  who  has  for  the  first  time  lifted  his  eyes 
to  the  nocturnal  sky,  and  beheld  the  moon  walking  in 
brightness  amid  the  planetary  orbs  and  the  host  of  stars, 
but  must  have  been  struck  with  admiration  and  wonder 
at  the  splendid  scene,  and  excited  to  inquiries  into  the 
nature  and  destination  of  those  far-distant  orbs.  Com- 
pared with  the  splendor,  the  amplitude,  the  august  mo- 
Uons,  and  the  ideas  of  infinity  which  the  celestial  vault 
presents,  the  most  resplendent  terrestrial  scenes  sink 
into  inanity,  and  appear  unworthy  of  being  set  in  com- 
petition with  the  glories  of  the  sky. 

"  When,  on  a  clear  autumnal  evening,  after  sunset, 
we  take  a  .serious  and  attentive  view  of  the  celestial 
canopy ;  when  we  behold  the  moon  displaying  her 
brilliant  crescent  in  the  western  sky  ;  the  evening  star 
gilding  the  shades  of  night ;  the  planets  moving  in  their 
several  orbits  ;  the  stars,  one  after  another,  emerging 
from  the  blue  ethereal,  and  gradually  lighting  up  the 
firmament  till  it  appears  all  over  spangled  with  a  bril- 
liant assemblage  of  shining  orbs  ;  and  particularly  w^en 
we  behold  one  cluster  of  stars  gradually  descending 
oelow  the  western  horizon,  and  other  clusters  emerging 
from  the  east,  and  ascending,  in  unison,  the  canopy  of 
heaven  ;  when  we  contemplate  the  whole  celestial  vault, 
with  all  the  shining  orbs  it  contains,  moving  in  silent 
grandeur,  like  one  vast  concave  sphere,  around  this 
lower  world  and  the  place  on  which  we  stand  —  such  a 


ASTRONO5TY.  11 

scene  naturally  leads  a  reflecting  mind  to  such  inquiries 
as  these  :  Whence  come  those  stars  which  are  ascend- 
ing from  the  east  ?  Whither  have  those  gone  which 
have  disappeared  in  the  west  ?  What  becomes,of  the 
stars,  during  the  day,  which  are  seen  in  the  night  ?  Is 
the  motion  which  appears  in  the  celestial  vault  reoZ,  or 
does  a  motion  in  the  Earth  itself  cause  this  appearance  ? 
What  are  those  immense  numbers  of  shining  orbs 
which  appear  in  every  part  of  the  sky  ?  Are  they 
mere  studs,  or  tapers,  fixed  in  the  arch  of  heaven,  or  are 
they  bodies  of  immense  size  and  splendor  ?  Do  they 
shiiie  with  borrowed  light,  or  with  their  own  native 
lustre  ?  Are  they  placed  only  a  few  miles  above  the 
region  of  the  clouds,  or  at  immense  distances,  beyond 
the  range  of  human  comprehension  ?  Can  their  dis- 
tance be  ascertained  ?  Can  their  bulk  be  computed  ? 
By  what  laws  are  their  motions  regulated — and  what 
purposes  are  they  destined  to  subserve  in  the  great  plan 
of  the  universe  ?  n 

These,  and  similar  questions,  it  is  the  province  of 
Astronomy  to  resolve,  so  far  as  human  intelligence  can 
compass  them.  Vast  as  is  the  subject,  and  far  as  it 
may  seem  beyond  our  reach,  yet  in  no  other  science 
have  there  been  such  gradual  and  constant  accessions 
of  knowledge  as  in  this.  It  may  at  the  same  time  be 
observed,  that  in  none  so  much  remains  to  be  dis- 
covered. Laplace,  who  knew  more  than  any  other 
man  of  the  mechanism  of  the  heavens,  said  earnestly, 
on  his  deathbed,  "  What  we  know  is  little  —  what 
we  do  not  know  is  immense."  The  same  feeling  was 
entertained  by  Newton,  at  the  moment  of  his  im- 
mortal discovery  of  the  principle  of  gravitation,  when, 


12 


ASTRONOMY. 


with  the  modesty  of  all  great  minds,  beside  whose 
infinite  aspirations  the  highest  possible  attainment  is 
ever  insignificant,  he  exclaimed,  "  I  am  but  as  a  child 
standing  upon  the  shore  of  the  vast,  undiscovered  o-,ean, 
and  playing  with  a  little  pebble,  which  the  waters  have 
washed  to  my  feet." 


THE   SOLAR  SYSTEM. 


Comparative  Size  of  tfie  larger  Planets. 

The  Solar  System  is  composed  of  a  great  central 
luminary,  the  Sun,  whose  mass  is  supposed  to  be  made 
up  of  opaque  matter,  like  the  Earth, —  the  atmosphere 
alone  being  luminous,  —  and  a  number  of  comparatively 
small  engirdling  bodies,  the  planets,  comets,  &c.,  which 
revolve  around  it  in  various  periods.  The  comparative 


ASTRONOMY.  13 

size  of  these  bodies,  and  their  respective  distances  from 
each  other,  may  be  estimated  by  the  following  illustra- 
tion. On  a  level  field,  place  a  globe,  two  feet  in  diam- 
eter ;  this  will  represent  the  SUN.  MERCURY  will  be 
represented  by  a  grain  of  mustard  seed,  on  the  circum- 
ference o.f  a  circle  164  feet  in  diameter ;  VENUS,  by  a 
pea,  on  a  circle  284  feet  in  diameter ;  the  EARTH,  a 
somewhat  larger  pea,  on  a  circle  of  430  feet ;  MARS,  a 
large  pin's  head,  on  a  circle  of  654  feet ;  JUNO,  CERES, 
VESTA,  and  PALLAS,  grains  of  sand,  in  orbits  of  from 
1000  to  1200  feet ;  JUPITER,  an  orange,  in  an  orbit  of 
nearly  half  a  mile  across  ;  SATURN,  a  small  orange,  in 
an  orbit  of  four  fifths  of  a  mile ;  and  URANUS,  a  cherry, 
on  the  circumference  of  a  circle  more  than  a  mile  and 
a  half  in  diameter.  We  shall  now  proceed  to  give  a 
more  particular  account  of  these  members  of  the  solar 
system. 

THE  SUN. 

The  Sun,  when  viewed  with  a  telescope,  presents  the 
appearance  of  an  enormous  globe  of  fire,  frequently  in 
a  state  of  violent  agitation  or  ebullition.  Black  spots, 
of  irregular  form,  rarely  visible  to  the  naked  eye,  some- 
times pass  over  his  disk,  in  a  space  of  about  fourteen 
days ;  one  was  measured  by  Sir  W.  Herschel,  in  1779, 
and  found  to  be  30,000  miles  in  breadth.  A  spot,  when 
first  seen  on  the  eastern  edge,  appears  like  a  line,  pro 
gressively  extending  in  breadth,  till  it  reaches  the  mid- 
dle, when  it  begins  to  contract,  and  ultimately  disap- 
pears at  the  western  edge.  In  some  rare  instances, 
spots  reappear  on  the  eastern  side,  and  are  even  per- 
manent for  two  or  three  revolutions ;  but  they  generally 
change  their  aspect  in  a  few  days,  and  disappear. 

xiii.— 2 


14  ASTRONOMY. 

Astronomers  inform  us,  that  sometimes  50  spots  are 
seen,  at  once,  on  the  Sun's  surface.  From  1611  to  1629, 
it  was  hardly  free  from  spots  ;  while  from  1650  to  1670, 
scarcely  any  were  to  be  seen.  The  same  irregularity 
has  been  frequently  noticed.  In  October,  1827,  150 
spots  were  noticed  at  one  time. 

Sometimes,  several  small  spots  unite  into  a  large  one ; 
again,  a  large  one  separates  into  smaller  ones,  which 
soon  vanish.  These  phenomena  induced  Herschel  to 
suppose  the  Sun  to  be  a  solid,  dark  nucleus,  surrounded 
by  a  vast  atmosphere,  almost  always  filled  with  lumi- 
nous clouds,  occasionally  opening  and  disclosing  the 
opaque  mass  within. 

The  speculations  of  Laplace  were  different ;  he 
imagined  the  solar  orb  to  be  a  mass  of  fire,  and  that 
the  violent  effervescences  and  explosions,  seen  on  its 
surface,  are  occasioned  by  the  eruption  of  elastic  fluids 
formed  in  its  interior  ;  and  that  the  spots  are  enormous 
caverns,  like  the  craters  of  our  volcanoes.  The  theory 
of  Herschel,  however,  is  that  most  generally  received 
by  learned  men. 

"  The  magnitude  of  this  vast  luminary  is  an  object 
which  overpowers  the  imagination.  Its  diameter  is 
880,000  miles  ;  its  circumference,  2,764,600  miles;  its 
surface  contains  2,432,800,000,000  of  square  miles, 
wLk'i  is  twelve  thousand  three  hundred  and  fifty  times 
the  srea  of  the  terraqueous  globe,  and  nearly  fifty 
then? and  times  the  extent  of  all  the  habitable  parts  of 
the  I3arth.  Were  its  centre  placed  over  the  Earth,  it 
would  fill  the  whole  orbit  of  the  moon,  and  reach  200,- 
0$0  •miles  beyond  it  on  every  hand.  Were  a  person  to 
tejrjl  along  the  surface  of  the  Sun,  so  as  to  pass  along 


ASTRONOMY.  15 

every  square  mile  on  its  surface,  at  the  rate  of  thirty 
miles  every  day,  it  would  require  more  than  two  hun- 
dred and  twenty  millions  of  years  before  the  survey  of 
this  vast  globe  could  be  completed. 

**  It  would  contain  within  its  circumference  more  than 
thirteen  hundred  thousand  globes  as  large  as  the  Earth, 
and  a  thousand  globes  of  the  size  of  Jupiter,  which  is 
the  largest  planet  of  the  system.  It  is  more  than  five 
hundred  times  larger  than  all  the  planets,  satellites,  and 
comets  belonging  to  our  system,  vast  and  extensive  as 
some  of  them  are.  Although  its  density  is  little  more 
than  that  of  water,  it  would  weigh  3360  planets  such 
as  Saturn,  1067  planets  such  as  Jupiter,  329,000  globes 
such  as  the  Earth,  and  more  than  2,000,000  of  globes 
such  as  Mercury,  although  its  density  is  nearly  equal  to 
that  of  lead." 

The  most  obvious  apparent  motion  of  the  Sun  is, 
that  it  seems  to  rise  in  the  morning  in  the  east;  to 
traverse  the  heavens  in  a  westerly  direction,  and  at  last 
to  disappear  beneath  the  horizon.  But  it  is  now  well 
understood  that  the  Sun  is  quiescent,  and  that  the  seem- 
ing motion  we  have  described  is  occasioned  by  the  daily 
rotation  of  the  Earth  on  its  axis.  But  although  the  Sun 
stands  in  the  centre  of  the  system  of  planets,  it  appears 
that  it  revolves  on  its  axis  like  the  other  heavenly  bodies, 
and  that  it  completes  its  revolution  in  twenty-five  days 
and  ten  hours.  Every  part  of  its  equator  moves  at 
the  rate  of  4352  miles  an  hour.  It  is  also  considered 
probable  that  the  Sun,  attended  by  its  troop  of  planets, 
makes  a  vast  journey  in  space,  but  whether  in  a  straight 
line,  or  in  an  immense  circle,  is  still  matter  of  conjec- 
ture. 


16  ASTRONOMY. 


THE  PLANET  MERCURY. 

This  planet  is  37,000,000  miles  from  the  Sun,  and  is 
the  nearest  that  has  yet  been  discovered.  It  is  seldom 
seen  by  the  naked  eye  ;  its  daily  revolution  is  performed 
in  24  hours,  5  minutes,  and  20  seconds.  It  revolves 
round  the  Sun  in  the  space  of  87  days  and  23  hours. 
When  viewed  with  the  telescope,  it  presents  the  various 
phases  of  the  moon,  from  a  crescent  to  the  full,  round 
orb. 

Few  discoveries  have  been  made  on  this  planet,  ow- 
ing to  the  dazzling  splendor  of  its  rays.  Mountains, 
however,  have  been  seen  ;  and  one  of  them  is  said  to 
be  upwards  of  ten  miles  in  height,  which  is  nearly  twice 
the  elevation  of  the  loftiest  peaks  on  our  globe.  The 
light  upon  its  surface  is  supposed  to  be  seven  times 
greater  than  upon  the  Earth.  If  the  planet  be  inhabited, 
it  is  obvious  that  the  organization  of  the  eye  must  be 
different  from  that  of  ours.  It  is  supposed  that  the  in- 
tensity of  heat  is  not  greater  than  with  us. 

The  diameter  of  Mercury  is  3200  miles.  Its  surface 
contains  32,000,000  of  square  miles.  It  is  about  one 
fifteenth  the  size  of  the  Earth. 

In  its  revolution  round  the  Sun,  its  motion  is  swifter 
than  that  of  any  other  planet,  being  109,800  miles 
every  hour,  1830  miles  every  minute,  and  more  than 
30  miles  during  each  beat  of  the  pulse.  The  density 
of  matter  composing  Mercury  is  twice  that  of  the 
Earth,  yet  it  would  require  two  millions  of  globes,  of 
the  same  size,  to  make  one  of  the  size  and  density  of 
the  Sun 


ASTRONOMY.  17 


THE  PLAKET  VESUS. 

With  the  exception  of  the  Sun  and  moon,  this  is 
the  most  splendid  of  the  heavenly  bodies.  It  appears 
like  a  shining  lamp  amid  the  lesser  orbs  of  night ;  and, 
at  particular  seasons,  ushers  in  the  morning  dawn  and 
the  evening  twilight.  But  if  such  is  its  appearance  to 
the  naked  eye,  it  becomes  a  still  more  interesting  ob- 
ject, when  viewed  with  the  telescope  of  the  astronomer. 
It  passes  through  all  the  phases  of  the  moon,  from 
the  crescent  to  the  gibbous  form ;  and  formerly  several 
dark  spots  were  noticed  upon  its  surface.  Its  daily  ro- 
tation is  performed  in  23  hours  and  20  minutes.  Sev- 
eral mountains  have  been  discovered,  and  one  of  them 
is  nearly  twenty  miles  high,  or  five  times  the  height  of 
Chimborazo.  It  possesses  an  atmosphere  supposed  to 
be  about  three  miles  in  height,  and  is  supposed  to  have 
a  satellite,  or  moon ;  but  this  is  not  determined  with 
certainty. 

The  diameter  of  Venus  is  7800  miles,  being  a  little 
less  than  that  of  the  Earth.  It  does  not  appear  that 
any  great  quantity  of  water  exists  upon  it  Its  quantity 
of  light  is  about  twice  that  of  the  Earth.  It  revolves 
in  an  orbit  of  433,800,000  miles,  in  the  space  of  224 
days  and  16  hours.  Its  distance  from  the  Sun  is 
68,000,000  miles,  and  from  the  Earth,  when  nearest  to 
us,  about  27,000,000  miles.  Its  matter  is  in  a  slight 
degree  less  dense  than  that  ot  the  Earth. 

TEE  EARTH. 

Although  the  Earth  appears  to  be  larger  than  all  the 
heavenly  orbs,  it  is,  in  fact,  infinitely  smaller,  and  holda 
2* 


18 


ASTRONOMY 


a  rank  with  the  inferior  bodies  of  the  universe.  Al 
though  it  appears  to  the  eye  of  sense  immovably  fixed, 
it  has  a  double  motion  —  one  on  its  own  axis,  and  one 
around  the  Sun,  by  which  it  is  transported,  with  all  its 
continents,  and  oceans,  and  kingdoms,  at  the  rate  of 
more  than  a  thousand  miles  a  minute. 


This  planet,  like  all  the  other  heavenly  bodies,  has  a 
globular  shape  ;  but  it  is  not  a  perfect  globe,  it  being  de- 
pressed at  the  poles.  The  diameter,  through  the  poles, 
is  34  miles  less  than  through  the  equator.  This  curious 
fact  was  discovered  by  perceiving  that  the  pendulum 
of  a  clock  had  140  vibrations  less  in  a  day,  at  Paris, 
than  at  Cayenne,  in  Guiana.  Further  observations  were 
made,  and  it  was  found  that  this  variation  was  uniform, 
and  that  the  vibrations  regularly  diminished  in  proceed- 
ing northward  from  the  equator.  This  led  to  many 
curious  investigations,  which  resulted  in  demonstrating 


ASTRONOMY.  19 

the  fact  we  have  above  mentioned.  It  is  interesting  to 
observe,  that  so  simple  a  circumstance  as  the  slower 
movement  of  clocks,  in  a  southern  latitude,  should 
have  led  to  so  wonderful  a  discovery  in  science  as  the 
depression  of  the  poles  of  the  Earth. 

The  prominent  feature  of  the  Earth's  surface  is  its 
division  into  land  and  water  ;  the  latter  predominates, 
occupying  148,000,000  square  miles,  or  more  than  two 
thirds  of  the  face  of  the  globe.  It  contains  296,000,000 
of  cubical  miles  of  water,  sufficient  to  cover  the  whole 
globe  to  the  depth  of  more  than  half  a  mile.  This 
superabundance  of  water  is  probably  peculiar  to  our 
planet,  and  is  conjectured  to  have  resulted  from  the 
deluge. 

The  surface  of  the  Earth  is  further  diversified  by 
ranges  of  mountains,  stretching  across  the  continents 
and  islands,  and  giving  variety  to  the  landscapes  of  every 
country.  From  these  mountains  flow  myriads  of  streams, 
fertilizing  the  valleys  through  which  they  take  their 
course,  and  at  last  losing  themselves  in  the  ocean.  An 
atmosphere,  about  100  miles  in  height,  surrounds  this 
terraqueous  mass,  which,  put  in  motion,  forms  the  winds, 
which  fan  the  earth  with  gentle  breezes,  or  heave  the 
ocean  into  billows.  It  is  the  theatre  where  the  light- 
nings flash,  and  the  thunders  roll ;  where  the  meteor 
sweeps  with  its  fiery  train,  and  the  Aurora  Borealis  dis- 
plays its  fantastic  coruscations. 

Were  the  Earth  viewed  from  some  point  in  the 
heavens  —  as  the  moon,  for  instance — it  would  have 
somewhat  the  same  appearance  as  the  moon  does  to  us. 
The  distinction  between  its  seas,  oceans,  continents, 


20  ASTRONOMY. 

and  islands,  would  be  clearly  marked,  and  would  appear 
like  brighter  or  darker  spots  upon  its  disk.  The  conti- 
nents would  appear  bright,  and  the  oceans  of  a  darker 
hue,  because  water  absorbs  a  great  part  of  the  solar 
rays  that  fall  upon  it. 


The,  Earth,  as  it  would  appear  from  the  Moon. 

We  are  quite  well  acquainted  with  the  surface  of  the 
Earth,  but  our  knowledge  of  its  internal  structure  is 
very  limited.  The  deepest  mine  does  not  extend  more 
than  a  mile  from  the  surface ;  and  this  depth,  compared 
with  the  diameter  of  the  Earth,  is  not  more  than  the 
scratch  of  a  pin  upon  the  surface  of  an  artificial  globe. 
What  materials  are  to  be  found  within  the  bowels  of 
the  Earth,  will  be  forever  beyond  the  power  of  mortals 
to  determine.  It  is  supposed,  however,  and  not  with- 
out reason,  that,  while  the  crust  of  the  globe  consists  of 


ASTRONOMY.  .  21 

a  framework  of  rocks,  mingled  with  earth  and  water, 
the  centre  is  occupied  with  a  vast  metallic  mass  in 
a  state  of  fusion  from  heat. 

The  density  of  the  whole  Earth,  bulk  for  bulk,  is 
estimated  at  five  times  the  weight  of  water,  so  that  it 
would  counterpoise  five  globes  of  water  of  the  same 
size.  The  diurnal  revolution  of  the  Earth  is  performed 
in  23  hours,  56  minutes.  This  gives  rise  to  day  and 
night ;  to  which  arrangement  of  nature,  the  economy 
of  the  vegetable  as  well  as  of  the  animal  world  is 
adjusted.  The  annual  revolution  of  the  Earth  is  ac-' 
complished  in  365  days,  5  hours,  45  minutes,  and 
51  seconds.  From  this  proceed  the  varieties  of  the 
seasons :  spring,  summer,  autumn,  and  winter,  follow 
each  other  in  constant  succession,  diversifying  the 
scenery  of  nature,  and  marking  the  different  periods 
of  the  year.  In  those  countries  which  lie  in  the  south- 
ern hemisphere  of  the  globe,  as  at  Buenos  Ayres  and 
the  Cape  of  Good  Hope,  December,  January,  and 
February,  are  the  summer  months,  while  in  this  north- 
ern hemisphere,  these  are  the  winter  months,  when  the 
weather  is  coldest  and  the  days  are  shortest. 

The  average  distance  of  the  Earth  from  the  Sun  is 
95,000,000  miles.  The  length  of  the  path  annually 
travelled  by  the  Earth  in  its  orbit  is  567,019,740  miles, 
or  about  1000  miles  a  minute,  or  17  miles  a  second. 

The  Moon,  a  satellite  of  our  own  planet,  is  the 
heavenly  body  of  which  we  have  the  most  accurate 
knowledge.  Its  surface  exhibits  a  very  large  number 
of  mountains,  almost  uniformly  of  a  circular  or  cusp- 
shaped  form,  the  larger  ones  having,  for  the  most 
part,  flat  bottoms  within,  from  which  rises,  in  the 


22  ASTRONOMY. 

centre,  a  small,  steep,  conical  hill.  They  offer,  in  its 
highest  perfection,  the  true  volcanic  character,  as  it 
may  be  seen  in  the  crater  of  Vesuvius.  In  some  of 
the  principal  ones,  decided  marks  of  volcanic  stratifica- 
tion, arising  from  successive  deposits  of  ejected  matter, 
may  be  clearly  traced  with  powerful  telescopes. 


Telescopic  Views  of  the  Moon. 

It  is,  moreover,  a  singular  fact  in  the  geology  of  the 
moon,  that,  although  nothing  like  water  can  be  per- 
ceived, yet  there  are  large  regions  perfectly  level,  and 
apparently  of  an  alluvial  character.  The  mountains  are 
known  by  their  shadows,  which  are  distinctly  visible, 
and  which  are  long  when  they  are  near  the  boundary 
of  light  and  darkness,  or  when  the  sun  is  in  the  horizon, 
and  disappear  when  they  are  90  degrees  from  that 
boundary,  or  when  the  sun  is  overhead. 

The  moon  is  generally  believed  either  to  have  no 
atmosphere,  or  one  of  such  tenuity  as  not  to  equal  in 


ASTRONOMY.  23 

density  the  contents  of  an  exhausted  receiver.  From 
this  it  has  been  inferred  that  there  are  no  fluids  at  the 
surface  of  the  moon  —  since,  if  there  were,  an  atmos- 
phere must  be  formed  by  evaporation.  Without  air 
and  water,  it  would  seem  that  the  moon  cannot  be 
inhabited ;  or,  if  life  exist  there,  it  cannot  be  in  any 
form  which  is  exhibited  in  our  own  planet.  The  days 
and  nights  in  the  moon  are  each  14  days  and  three 
quarters  in  length:  the  intense  heat  and  cold  which 
must  thus  alternate  would  destroy  human  life,  even 
on  the  supposition  that  vegetation  could  be  maintained.* 
The  moon,  like  all  other  heavenly  bodies,  appears  to 
rise  in  the  east  and  set  in  the  western  part  of  the 
horizon.  Its  real  motion,  however,  is  in  a  contrary 
direction  —  that  is,  from  west  to  east,  or  in  the  same 
direction  in  which  all  the  planets  move  round  the  Sun. 
It  is  a  dark  body,  deriving  its  light  from  the  Sun,  and 
occasionally  a  faint  light,  by  reflection  of  the  Sun's 
rays,  from  the  Earth.  It  is  about  240,000  miles  from 
the  centre  of  the  Earth,  and  pursues  its  course  around 
this  planet  at  the  rate  of  2300  miles  an  hour.  It 

*  Such  are  the  conclusions  of  most  philosophers.  Yet  Dr. 
Dick  observes,  that  "  probably  the  moon  is  surrounded  with 
a  fluid  which  serves  the  purpose  of  an  atmosphere,  though 
it  may  be  different  in  its  nature  and  composition  from  that 
which  surrounds  the  earth."  He  hence  concludes  that  the 
moon  may  be  inhabited,  and,  indeed,  proceeds  to  assume  this 
as  the  fact.  Upon  this,  he  makes  a  great  variety  of  ingenious 
suggestions,  and  even  supposes  it  to  be  possible  to  trace  the 
operations  of  intelligent  beings  upon  its  surface.  Dr.  Olbers  is 
also  of  the  opinion,  that  the  moon  is  inhabited  by  rational 
creatures,  and  that  its  surface  is  covered  with  vegetation  not 
very  dissimilar  to  that  of  our  Earth. 


24 


ASTRONOMY. 


performs  its  revolution  in  29  days,  12  hours,  and  44 
minutes.  It  is  a  curious  fact,  that  the  revolution  on 
its  axis  is  performed  in  the  same  time  as  its  revolu- 
tion round  the  Earth.  Accordingly,  it  always  presents 
the  same  face  to  the  Earth,  so  that  we  never  see  more 
than  one  side  of  it. 

The  moon  appears  nearly  as  large  as  the  Sun  ;  but  it 
is  but  about  one  fiftieth  the  size  of  the  Earth,  and  it 
would  take  63,000,000  of  globes,  of  the  size  of  the 
moon,  to  make  one  of  the  Sun. 


An  Eclipse  of  the  Sun. 

When  the  Earth  comes  between  the  S»n  and  moon, 
it  casts  its  shadow  upon  the  latter,  which  is  then  said  to 
be  eclipsed.  An  eclipse  of  the  Sun  is  occasioned  by 
the  moon  coming  between  the  Earth  and  the  Sun,  thus 
cutting  off  its  rays.  An  eclipse  of  the  moon  always 
occurs  at  the  time  of  its  full ;  eclipses  of  the  Sun 
occur  at  the  time  of  the  new  moon.  It  is  one  of  the 


ASTRONOMY.  25 

triumphs  of  science,  that  these  sublime  phenomena, 
formerly  so  fruitful  a  source  of  superstitious  fear  and 
ominous  prediction,  are  now  the  subject  of  the  most  ex- 
act calculation,  and  are  as  much  divested  of  every  mys- 
terious attribute,  as  the  common  events  of  sunrise  and 
sunset. 

THE  PLANET  MARS. 


Telescopic  Appearances  of  Mars. 

The  Earth  is  placed,  in  the  solar  system,  between  the 
orbits  of  Venus  and  Mars.  The  latter  is  145,000,000 
miles  from  the  Sun.  When  nearest  the  Earth,  its  dis- 
tance is  50,000,000 ;  when  farthest,  240,000,000  miles. 
This  fact  will  explain,  what  most  persons  have  noticed, 
that  this  planet  is  at  one  time  almost  imperceptible,  and 
at  another  seems  to  vie  with  Jupiter  in  magnitude  and 
splendor.  The  diurnal  revolution  of  Mars  is  performed 
in  24  hours,  39  minutes,  29  seconds.  Its  orbit  is 
900,000,000  miles  in  circumference.  It  performs  this 
circuit  in  1  year  and  322  days.  Its  rate  of  motion  is 
54,649  miles  every  hour,  which  is  more  than  a  hundred 
times  greater  than  the  utmost  velocity  of  a  cannon-ball 

When  viewed  through  a  telescope,  this  planet  pre- 
xiii. — 3 


2O  ASTRONOMY. 

sents  a  variety  of  dark  spots  and  belts,  though  of 
different  forms  and  shades.  Luminous  spots,  and  zones, 
have  also  been  discovered,  which  frequently  change 
their  appearance,  and  alternately  disappear  and  return. 
The  latter  are  supposed  to  be  occasioned  by  snow  ;  the 
former  are  conjectured  to  be  occasioned  by  a  distribu- 
tion of  the  face  of  the  planet  into  land  and  water.  It  is 
supposed  that  one  third  of  the  surface  is  occupied  by 
the  latter.  It  is  probable  that  the  diversities  in  the 
appearance  of  Mars,  as  seen  through  a  telescope,  are 
in  part  occasioned  by  clouds. 

Mars  has  a  variety  of  seasons,  similar  to  ours,  and  it 
bears  a  closer  resemblance  to  the  Earth  than  any  other 
planet.  It  is  4200  miles  in  diameter,  a  little  more  than 
half  that  of  our  globe.  No  moon  or  satellite  has  been 
discovered,  as  attendant  upon  it. 

CERES,  PALLAS,  JUNO,  AJND  VESTA. 

The  immense  interval  which  lies  between  the  orbits 
of  Mars  and  Jupiter  had  led  the  astronomers  to  surmise 
that  some  planet,  of  considerable  magnitude,  might  pos- 
sibly exist  within  this  limit.  But  instead  of  one,  four 
small  orbs  have  been  recently  discovered,  which  bear 
the  above  names.  The  first,  called  Ceres,  was  discov- 
ered by  Piazzi,  in  Sicily,  on  the  first  day  of  the  present 
century.  Pallas  was  discovered  in  March,  1802,  by 
Olbers ,  Juno  by  Harding,  in  September,  1804,  and 
Vesta  by  Olbers,  in  March,  1807. 

These  four  planets  are  invisible  to  the  naked  eye, 
and  we  are,  therefore,  indebted  to  the  telescope  for  a 
knowledge  of  their  existence.  It  is  conjectured,  and 
not  without  reason,  that  these  four  planets, were  once 


ASTRONOMY.  27 

united  in  one,  and  that  by  some  mighty  force  they  have 
been  sundered,  and  thrown  into  their  present  orbits. 
Their  diameter  has  not  been  ascertained  with  precision. 
Herschel  reckons  that  the  largest  does  not  exceed  500 
miles  in  circumference.  In  several  respects,  they  are 
marked  with  peculiarities.  The  orbits  of  some  of 
them  cross  each  other,  which  is  not  the  case  with  any 
other  planet.  They  revolve  in  nearly  the  same  mean 
distances  from  the  Sun, — that  is,  about  260,000,000 
miles.  Their  annual  revolutions,  also,  are  nearly  the 
same ;  being  little  more  than  four  years.  They  are 
smaller  than  the  other  planets — Ceres  containing  but 
one  eighth  part  as  many  solid  miles  as  Mercury.  It  is 
probable  that  they  are  even  smaller  than  the  moons  of 
Jupiter,  Saturn,  or  Uranus. 

THE  PLANET  JUPITER. 


Tdtscopie  View,  of  Jupiter. 

We  now  come  to  one  of  the  most  splendid  orbs  in 
the  planetary  system.  Jupiter  is  495,000,000  miles 
from  the  Sun,  and  the  circumference  of  its  orbit  is 
3,1 10,000,000  of  miles.  Around  this  orbit  it  moves  in 
11  years,  315  days,  at  the  rate  of  about  30,000  miles 


28  ASTEONOMY. 

an  hour.  Its  nearest  approach  to  the  Earth  is  about 
600,000,000  miles.  A  cannon-ball,  flying  at  the  rate 
of  500  miles  an  hour,  would  reach  it  in  a  little  less 
than  a  hundred  years.  The  daily  rotation  of  Jupiter  is 
performed  in  9  hours,  59  minutes,  49J  seconds.  Its 
circumference  is  278,600  miles.  Its  density  is  a  little 
more  than  that  of  water,  or  five  times  less  than  that  of 
the  Earth.  It  is  the  largest  planet  in  our  system,  being 
1400  times  larger  than  the  Earth. 

When  viewed  with  a  powerful  telescope,  this  planet 
presents  a  splendid  appearance.  Its  surface,  then, 
seems  larger  than  the  full  moon  to  the  naked  eye.  Its 
disk  is  diversified  with  darkish  parallel  stripes.  The 
four  satellites,  revolving  around  the  planet,  generally 
appear  in  a  straight  line  with  each  other.  Sometimes, 
only  two  of  them  are  visible,  the  other  two  being 
eclipsed  either  by  the  disk  or  the  shadow  of  Jupiter ; 
at  other  times,  all  are  seen  at  once.  From  their 
changing  appearance,  it  it  supposed  that  the  dark  belts 
of  Jupiter  are  the  body  of  the  planet,  seen  through 
something  analogous  to  clouds,  floating  in  its  atmos- 
phere at  a  considerable  elevation  above  its  surface. 

The  day  and  night  in  Jupiter  are  nearly  equal.  The 
intensity  of  its  solar  light  is  27  times  less  than  that  of 
the  Earth.  It  is  greatly  depressed  at  the  poles ;  the 
diameter  of  the  equator  being  6,300  miles  greater  than 
that  at  the  poles. 

THE  PLANET   SATURN. 

This  planet  may  be  considered  in  many  respects  the 
most  magnificent  and  interesting  body  within  the  limits 
of  the  planetary  system.  Taking  into  view  its  satellites 


ASTRONOMY.  29 

and  rings,  it  has  a  greater  quantity  of  surface  than 
even  the  globe  of  Jupiter ;  and  its  majestic  rings  con- 
stitute the  most  singular  and  astonishing  phenomena 
that  have  yet  been  discovered  in  the  sidereal  universe. 

Its  distance  from  the  Sun  is  906,000,000  of  miles, 
which  is  nearly  twice  the  distance  of  Jupiter,  or  ten 
times  that  of  the  Earth.  The  circumference  of  its 
orbit  is  5,695,000,000  of  miles.  When  nearest,  it  is 
811,000,000  of  miles  from  the  Earth.  A  steam  car- 
riage, travelling  at  the  rate  of  20  miles  an  hour,  would 
not  reach  it  in  less  than  4629  years. 

This  planet  revolves  round  the  Sun  in  the  space  of 
about  29£  years.  Its  motion  is  at  the  rate  of  22,000 
miles  an  hour.  Its  diurnal  rotation  is  performed  in  10 
hours,  29  minutes,  and  17  seconds.  This  rotation  is 
perpendicular  to  the  plane  of  its  rings.  Its  proportion 
of  light  from  the  Sun  is  but  one  90th  of  our  own.  It 
is  79,000  miles  in  diameter,  and  nearly  a  thousand 
times  larger  than  the  Earth.  When  viewed  with  a 
telescope,  it  exhibits  belts  similar  to  those  of  Jupiter, 
and  disposed  in  lines  parallel  to  the  ring.  These  are 
permanent,  and  probably  indicate  a  diversity  of  surface, 
either  of  land  or  water,  or  some  substance  with  which 
we  are  unacquainted.  Its  figure  is  spheroidal,  with 
considerable  polar  depressions. 

The  density  of  Saturn  is  about  the  same  as  cork,  or 
one  half  that  of  water.  This  is  taking  into  view  its 
whole  bulk ;  if  its  centre  is  hollow,  its  exterior  parts 
may  be  as  hard  as  rock.  It  has  been  said,  that  "  while 
a  native  of  earth  could  hardly  move  upon  Mercury, 
from  the  strong  attractive  power  pulling  him  to  the 
ground,  he  could,  on  the  planet  Saturn,  leap  sixty  feet 
3* 


30  ASTRONOMY. 

high  as  easily  as  he  could  here  leap  a  yard."  These 
suppositions  are,  however,  unsound.  The  density  of 
Mercury  is  double  that  of  the  Earth,  and  nearly  that 
of  lead  ;  but  it  must  be  considered  that  the  attraction 
in  the  planets  is  somewhat  in  proportion  to  the  masses 
of  matter  which  they  contain,  and  not  in  proportion  to 
their  density.  Taking  this  principle  into  view,  the 
attraction  upon  the  surface  of  Saturn  is  a  little  greater 
than  that  of  the  Earth.  It  is  supposed  that  there  is  no 
planet  in  the  solar  system,  with  the  exception  of  Ju- 
piter, on  which  an  inhabitant  of  the  Earth  might  not 
move  about  as  easily  as  upon  our  globe  ;  and  on  Jupi- 
ter, he  would  experience  little  more  than  double  the 
weight  he  now  feels. 

One  of  the  most  astonishing  phenomena  that  have 
yet  been  discovered  in  the  heavens,  is  the  double  ring 
of  Saturn.  As  generally  observed,  we  have  a  side 
view,  in  which  case  it  presents  nearly  the  following 
appearance. 


The  outside  diameter  of  the  exterior  ring  is  179,000 
miles ;  the  outside  diameter  of  the  interior  ring  is 
152,000  miles.  The  breadth  of  the  dark  space  be- 
tween the  two  rings  is  1800  miles ;  so  that  a  body 
nearly  as  large  as  our  moon  could  pass  through  it. 
The  breadth  of  the  exterior  ring  is  7200  miles ;  of  the 
interior,  20,000  miles.  The  thickness  of  the  ring  is 


ASTRONOMY.  31 

not  supposed  to  be  over  100  miles.  When  it  is 
presented  edgewise  to  the  earth,  it  can  only  be  seen 
with  a  powerful  glass.  This  ring  is  not  exactly  cir- 
cular, but  slightly  elliptical.  It  is  ascertained  to  have 
a  swift  rotation  around  Saturn,  which  is  completed  in 
about  10  hours  and  a  half.  The  outer  edge  of  the 
ring  is  550,000  miles  in  circumference,  and  moves  at 
the  rate  of  more  than  1000  miles  a  minute. 

This  double  ring  is  a  compact,  solid  substance,  for 
its  shadow  is  distinctly  seen  on  the  planet  which  it 
encloses.  It  is  not  certain  that  both  parts  of  the  ring 
have  exactly  the  same  periods  of  rotation.  It  is  about 
30,000  miles  from  the  surface  of  the  planet,  always 
keeps  the  same  relative  position,  and  attends  it  in  all  its 
movements.  One  side  of  it  contains  146  times  the 
surface  of  the  whole  of  our  globe  ! 

These  rings  will  appear,  to  the  inhabitants  in  the 
firmament  of  Saturn,  like  large  luminous  circles  or 
semicircles  of  light,  stretching  across  the  heavens 
from  east  to  west,  and  occupying  one  fourth  part  of 
the  sky.  As  they  are  brighter  than  the  body  of  the 
planet,  it  is  probable  that  they  are  of  some  substance 
which  is  fitted  to  reflect  the  solar  light  with  peculiar 
splendor.  How  glorious,  and  diversified,  must  be  the 
celestial  scenery  thus  presented  ! 

Saturn  has  seven  satellites,  all  revolving  beyond  its 
ring.  The  nearest  is  18,000  miles  beyond  its  exterior 
edges;  the  most  distant  is  2,297,000  miles  from  the 
planet,  and  performs  its  circuit  in  about  79J  days. 
The  largest  is  supposed  to  be  about  the  size  of  Mars, 
or  4200  miles  in  diameter.  These  satellites  must 
afford  a  splendid  appearance  from  the  planet,  as  some 
of  them  must  seem  nine  times  larger  than  our  moon. 


32  ASTRONOMY. 

If  we  take  this  into  view,  in  connection  with  the  sub- 
lime splendor  of  the  rings,  it  might  almost  seem  that 
Saturn  is  fitted  up  to  be  the  abode  of  some  favored 
beings,  upon  whom  the  Creator  has  lavished  the  won- 
ders of  his  creative  power. 

THE  PLANET  JJRANUS. 

This  planet,  also  frequently  called  after  its  discov- 
erer, was  made  known  to  us  by  Herschel,  who  first 
saw  it  in  March,  1781.  Its  distance  from  the  Sun  is 
1,800,000,000  miles ;  and  when  nearest  the  Earth,  it  is 
nearly  the  same  distance  from  us.  It  moves  through 
its  orbit  in  about  84  years.  It  is  the  slowest-moving 
planet  in  the  system,  yet  pursues  its  course  at  the  rate 
of  1500  miles  an  hour.  It.  is  110,000  miles  in  circum- 
ference, and  81  times  larger  than  the  Earth.  Its  solar 
light  is  360  times  less  than  ours  ;  yet  it  is  not  darker  than 
frequently  happens  with  us  in  a  cloudy  day.  Its  den- 
sity is  nearly  equal  to  that  of  water.  Six  satellites  are 
supposed  to  be  connected  with  this  planet ;  but  their 
periods  and  other  phenomena  have  not  yet  been 
accurately  ascertained. 

GENERAL  REMARKS  ON  THE  PLANETS. 

The  planets  all  move  from  west  to  east,  and  nearly  in 
the  same  plane.  They  are  all  opaque  bodies,  deriving 
their  light  from  the  Sun  ;  'they  are  all  spheroidal,  ap- 
proaching the  form  of  an  exact  globe,  with  slight 
unevenness  of  surface.  They  have  all  two  motions  ; 
one  diurnal,  around  their  axes,  and  one  annual,  around 
the  Sun.  They  all  present  every  part  of  their  surface 
toward  the  Sun,  and  they  have  the  alternate  change 
of  day  and  night.  They  are  all  connected  with  the  Sun 


ASTEOXOMY.  33 

by  the  same  principle  of  gravitation.  As  we  know 
that  our  Earth  is  inhabited  by  thousands  of  sentient 
beings,  and  was  created  for  their  accommodation,  we 
may  justly  conclude  that  other  worlds,  associated  in  the 
same  system,  fitted  up  in  nearly  the  same  manner, 
and  acting  in  obedience  to  the  same  great  laws, 
have  a  similar  design,  and  are,  therefore,  the  abodes 
of  myriads  of  intelligences  not  essentially  differing 
from  the  races  on  this  Earth. 

The  stupendous  scale  upon  which  planets  are  formed 
—  their  mighty  masses  —  their  amazing  circuits  per- 
formed in  the  regions  of  space  —  their  almost  incon- 
ceivable velocities  —  still  sink  into  insignificance, 
when  compared  with  the  enormous  bulk  of  the  great 
central  luminary  around  which  they  revolve.  In  order 
to  aid  the  imagination  in  its  efforts  to  compass  this 
subject,  Dr.  Dick  makes  the  following  suggestion :  — 

"  There  is  no  point  on  the  surface  of  the  globe  that 
unites  so  many  awful  and  sublime  objects  as  the  top  of 
Etna,  and  no  imagination  has  dared  to  form  an  idea  of 
so  glorious  and  magnificent  a  scene.  The  body  of  the 
Sun  is  seen  rising  from  the  ocean,  immense  tracts  both 
of  sea  and  land  intervening ;  the  islands  of  Pinari, 
Alicudi,  Lipari,  Stromboli,  and  Volcano,  with  their 
smoking  summits,  appear  under  your  feet,  and  you 
look  down  on  the  whole  of  Sicily  as  on  a  map,  and  can 
trace  every  river  through  all  its  windings  from  its 
source  to  its  mouth.  The  view  is  absolutely  boundless 
on  every  side,  so  that  the  sight  is  every  where  lost  in 
the  immensity. 

"  Yet  this  glorious  and  expansive  prospect  is  com- 
prised within  a  circle  about  240  miles  in  diameter,  and 


34  ASTRONOMY. 

754  in  circumference,  containing  45,240  square  miles, 
which  is  only  •girrTVB'TTF  Par':  °^  the  surface  of  the  Sun ; 
so  that  fifty-three  millions,  seven  hundred  and  seventy- 
six  thousand  landscapes,  such  as  beheld  from  Mount 
Etna,  must  pass  before  us  before  we  could  contem- 
plate a  surface  as  expansive  as  that  of  the  Sun ;  and 
if  every  such  landscape  were  to  occupy  two  hours  in 
the  contemplation,  as  supposed  above,  it  would  require 
24,554  years  before  the  whole  surface  of  this  immense 
globe  could  be  in  this  manner  surveyed." 

The  same  writer  here  quoted,  and  to  whom  we  are 
largely  indebted  in  the  preparation  of  this  article,  says, 
that  "  it  is  owing  to  the  existence  of  the  Sun  that  our 
globe  is  a  habitable  world,  and  productive  of  enjoyment. 
Almost  all  the  benign  agencies  which  are  going  for- 
ward in  the  atmosphere,  the  waters,  and  the  earth, 
derive  their  origin  from  its  powerful  and  perpetual 
influence.  Its  light  diffuses  itself  over  every  region, 
and  produces  all  that  diversity  of  coloring  which  en- 
livens and  adorns  the  landscape  of  the  world,  and 
without  which  we  should  be  unable  to  distinguish  one 
object  from  another.  By  its  vivifying  action,  vege- 
tables are  elaborated  from  inorganic  matter,  the  sap 
ascends  through  their  myriads  of  vessels,  the  flowers 
glow  with  the  richest  hues,  the  fruits  of  autumn  are 
matured,  and  become,  in  their  turn,  the  support  of 
animals  and  of  man. 

"  By  its  heat,  the  waters  of  the  rivers  and  the  ocean 
are  attenuated,  and  carried  to  the  higher  regions  of  the 
atmosphere,  where  they  circulate  in  the  form  of  vapor, 
till  they  again  descend  in  showers,  to  supply  the  sources 
of  the  rivers,  and  to  fertilize  the  soil.  By  the  same 
qgency  all  winds  are  produced,  which  purify  the  atmos- 


ASTRONOMY.  35 

phere  by  keeping  it  in  perpetual  motion,  which  propel 
our  ships  across  the  ocean,  dispel  noxious  vapors,  pre- 
vent p<  stilential  effluvia,  and  rid  our  habitations  of  a 
thousand  nuisances.  By  its  attractive  energy,  the  tides 
of  the  ocean  are  modified  and  regulated,  the  Earth 
conducted  in  its  annual  course,  and  the  moon  sustained 
and  directed  in  her  motions.  Its  influence  descends 
even  to  the  mineral  kingdom,  and  is  felt  in  the  chem- 
ical compositions  and  decompositions  of  the  elements 
of  nature. 

"  The  disturbances  in  the  electric  equilibrium  of  the 
atmosphere,  which  produce  the  phenomena  of  thunder, 
lightning,  and  rain,  and  the  varieties  of  terrestrial  mag- 
netism ;  the  slow  degradation  of  the  solid  constituents 
of  the  globe,  and  their  diffusion  among  the  waters  of 
the  ocean,  may  all  be  traced,  either  directly  or  indirectly, 
to  the  agency  of  the  Sun.  It  illuminates  and  cheers  all 
the  inhabitants  of  the  Earth,  from  the  polar  regions  to 
the  torrid  zone.  When  its  rays  gild  the  eastern  hori- 
zon, after  the  darkness  of  the  night,  something  like  a 
new  creation  appears.  The  landscape  is  adorned  with 
a  thousand  shades  and  colors;  millions  of  insects 
awake  and  bask  in  its  rays ;  the  birds  start  from  their 
slumbers,  and  fill  the  groves  with  their  melody ;  the 
flocks  and  herds  express  their  joy  in  hoarser  acclama- 
tions ;  *  man  goeth  forth  to  his  work  and  to  his  labor ;  * 
all  nature  smiles,  and  '  the  hills  rejoice  on  every  side.' 
Without  the  influence  of  this  august  luminary,  a  uni- 
versal gloom  would  ensue,  and  surrounding  worlds, 
with  all  their  trains  of  satellites,  would  be  shrouded  in 
perpetual  darkness.  This  Earth  would  become  a  life- 
less mass,  a  dreary  waste,  a  rude  lump  of  inactive 
matter,  without  beauty  or  order.'' 


ASTRONOMY. 


COMETS. 


None  of  the  heavenly  bodie*s  have  been  regarded 
with  more  interest  than  the  comets,  those  wandering 
and  mysterious  bodies  which,  in  remote  ages,  were 
beheld  with  superstitious  terror.  They  have  been 
imagined  to  portend  war,  pestilence,  famine,  and  the 
death  of  monarchs  ; '  to  be  the  vehicles  in  which  de- 
parted souls,  released  from  the  care  of  guardian  angels, 
were  transported  to  heaven ;  to  have  been  the  cause  of 
the  deluge  ;  to  reenforce  the  light  and  heat  of  the  sun  ; 
to  break  up  large  planets  into  smaller  ones ;  to  change 
the  climate  of  countries ;  to  introduce  epidemic  disorders ; 
and,  finally,  to  threaten  our  globe  with  total  destruction. 


.  ASTRONOMY.  37 

A  great  comet  is  indeed  an  object  well  calculated  to 
impress  every  beholder  with  astonishment  and  awe. 
Comets  have  been  known  with  tails  extending  from  the 
zenith  to  the  horizon,  while  the  disk  of  the  body  itself 
was  equal  in  size  to  the  full  moon.  The  belief  which 
prevailed  for  a  long  time  with  regard  to  the  nature  of 
these  bodies,  was,  that  they  were  meteors  of  temporary 
duration,  engendered  in  die  atmosphere  of  the  Earth. 
Some  circumstances,  certainly,  gave  a  degree  of  plausi- 
bility to  this  supposition ;  the  suddenness,  in  many  cases, 
of  their  appearance  and  disappearance,  the  transpa- 
rency of  their  tails,  and  the  apparently  small  density  of 
their  bodies.  But  accurate  observations  showed  that 
they  were  far  beyond  the  region  of  the  moon,  render- 
ing it  clear  that  they  could  not  be  vapors  generated  in 
our  atmosphere,  and  giving  a  strong  probability,  to  the 
opinion  maintained  of  old  by  the  Chaldeans,  and  sup- 
ported by  Seneca,  that  they  were  bodies  permanent  as 
the  planets  of  our  system,  and  reappearing  at  certain 
intervals,  depending  on  their  peculiar  orbits. 

It  is  probable  that  comets  are  nothing  but  bodies 
of  gas  or  vapor,  without  any  solid  matter  whatever. 
Stars  have  been  repeatedly  seen  through  their  thick- 
est parts.  The  mechanical  effect,  therefore,  to  the 
Earth,  from  its  collision  with  a  comet,  would  be  no 
greater  than  that  of  a  mountain  when  in  contact  with  a 
cloud :  the  result  of  such  a  collision  would  be  the  mix- 
ture of  the  gaseous  matter  with  the  Earth's  atmosphere  ; 
a  permanent  rise,  perhaps,  in  the  mean  height  of  the 
barometer ;  and,  if  the  gaseous  matter  should  condense 
sufficiently  to  descend  to  the  lower  regions  of  our  at- 
mosphere, some  effect  upon  animal  or  vegetable  exist- 
xni.— 4 


38  ASTRONOMY. 

ence,  good  or  bad.  The  Earth  may  actually  have  been 
many  times  in  the  tail  of  a  comet,  without  having  any 
strong  marks  of  such  an  accident. 

The  bodies  of  comets  have  varied  from  30  to  3000 
miles  in  diameter  ;  some  of  them  have  been  entirely 
destitute  of  tails,  and  others  have  exhibited  them 
100,000,000  of  miles  in  length.  They  move  in  nar- 
row, elliptical  orbits,  travelling  to  an  immense  distance 
out  of  our  system,  and  at  their  return  approaching,  ^n 
most  cases,  much  nearer  to  the  Sun  than  any  of  the 
planets.  Of  three  of  them  the  periodical  revolution 
has  been  ascertained.  Encke's  comet  revolves  in 


Encke's  Comet. 

three  years  and  a  half;  Biela's  in  six  and  three  quar- 
ters; and  Hal  ley's  in  seventy-five  years  and  a  half ; 
the  last  of  these  made  its  appearance  in  1835.  A 
comet  with  a  tail  of  uncommon  magnitude,  but  with  a 
nucleus  scarcely  perceptible,  visited  us  in  1843.  The 
great  comet  of  1680,  when  at  its  perihelion,  or  point 
nearest  the  Sun,  was  only  at  the  distance  of  one  sixth 
of  his  diameter  from  that  great  body  of  fire ;  it  conse- 


ASTRONOMY.  39 

quently  was  exposed  to  a  heat  27,500  times  greater 
than  that  received  by  the  Earth — a  degree  so  intense 
as  to  convert  into  vapor  every  terrestrial  substance  with 
which  we  are  acquainted.  One  hundred  and  forty 
comets  have  appeared  within  the  Earth's  orbit  during 
the  last  century,  which  have  not  again  been  seen.  If  a 
thousand  years  be  allowed  as  the  average  period  of 
each,  it  may  be  computed,  by  the  theory  of  probabil- 
ities, that  the  whole  number  ranging  within  the  Earth's 
orbit  must  be  1400.  But  Uranus  being  twenty  times 
more  distant,  there  may  be  no  less  than  11,200,000 
comets  that  come  within  the  known  extent  of  our 
system. 

The  trams  of  comets  are  always  thrown  off  in  a 
direction  opposite  to  the  Sun.  No  satisfactory  solution 
of  the  nature  and  cause  of  these  has  been  assigned. 
The  effect  is  the  same  as  if  the  nucleus  of  the  comet 
were  a  globe  of  water,  and  the  Sun,  in  shining  through 
it,  cast  its  refracted  rays  to  a  distance  beyond. 

THE  FIXED  STARS. 

Such  is  a  brief  description  of  the  solar  system,  which, 
down  to  the  beginning  of  the  present  century,  com- 
orised  within  its  limits  almost  the  whole  of  astronom- 
>cal  science.  Before  this  period,  the  planetary  orbits 
.seemed  to  encircle  all  the  space  accessible  to  the 
human  eye ;  they  had  effectively  established  limits  to 
systematic  inquiry ;  for  astronomers  had  never  pushed 
their  researches  into  remoter  depths,  having,  like  the 
uninstructed  multitude,  gazed  at  the  farther  heavens 
with  vague  and  incurious  glances,  content  to  admire 
their  beauty  and  confess  their  mystery.  This  period, 


40  ASTRONOMY. 

however,  was  distinguished  by  two  events  which  could 
not  have  existed  in  combination  without  leading  to 
important  results.  The  telescope,  formerly  of  very 
limited  range,  suddenly  assumed  a  capability  of  sound- 
ing immense  profundities  of  space ;  and  the  man  in 
whose  hands  it  attained  this  ne\v  power  was  possessed 
of  a  genius  adequate  to  improve  the  highest  opportu- 
nities. The  life  of  Sir  William  Herschel  marks  the 
first  and  greatest  epoch  of  modern  astronomy.  He 
was  a  discoverer  of  the  first  rank :  mingling  boldness 
with  a  just  modesty,  a  thirst  after  large  and  general 
views  with  a  habit  of  scrupulous  obedience  to  the  intima- 
tions of  existing  analogies,  he  was  precisely  the  man  to 
quit  paths  which,  through  familiarity,  were  common  and 
safe,  and  to  guide  us  into  regions  dim  and  remote, 
where  the  mind  must  be  a  lamp  to  itself. 

Herschel  communicated  to  the  world  the  first  proof 
that  there  existed  in  the  universe  organized  systems 
besides  our  own  ;  while  his  magnificent  speculations  on 
the  Milky  Way,  and  the  constitution  of  the  Nebulse,  first 
opened  the  road  to  the  conception  that  what  was  called 
the  universe  might  be,  and  in  all  probability  is,  but  a  de- 
tached and  minute  portion  of  that  interminable  series  of 
similar  formations  which  ought  to  bear  the  same  name. 

But  before  we  pursue  this  topic  farther,  it  will  be 
necessary  to  give  an  account  of  the  FIXED  STARS,  or 
that  stellar  firmament  to  which  the  solar  system  be- 
longs. About  2000  of  these  stars  are  visible  to  the 
naked  eye;  but  when  we  view  the  heavens  with  a 
telescope,  their  number  seems  to  be  limited  only  by 
the  imperfection  of  the  instrument.  In  one  hour  Sir 
William  Herschel  estimated  that  50,000  stars  passed 


ASTROXOMT. 


Find  Stars. 

through  the  field  of  his  telescope  in  a  zone  of  the 
heavens  two  degrees  in  breadth.  It  has  been  calcu- 
lated that  the  whole  expanse  of  the  heavens  must 
exhibit  about  100,000,000  of  fixed  stars,  within  the 
reach  of  telescopic  vision.  These  .stars  are  classed 
According  to  their  apparent  brightness ;  and  the  places 
of  the  most  remarkable  of  those  visible  to  the  naked 
eye,  are  ascertained  with  great  precision  and  formed 
into  a  catalogue.  Tb£  whole  number  of  stars  regis- 
tered amounts  to  about  200,000.  The  distance  of 
the  fixed  stars  is  too  great  to  admit  of  their  exhibit- 
ing a  perceptible  disk.  With  a  fine  telescope,  they 
appear  like  mere  luminous  points.  Their  twinkling 
arises  from  sudden  changes  in  the  refractive  power 
of  the  air,  which  would  not  be  sensible  to  the  eye  if 
they  had  disks,  like  the  planets.  Thus  we  can  learn 
nothing  of  the  relative  distances  of  the  fixed  stars  from 
us,  and  from  one  another,  by  their  apparent  diameters ; 
4* 


42  ASTRONOMY. 

but  as  they  do  not  appear  to  change  their  position 
during  the  passage  of  the  Earth  from  one  extremity  of 
its  orbit  to  the  other,  it  is  evident  that  we  must  be  more 
than  200,000,000  miles  distant  from  the  nearest.  Many 
of  them,  however,  must  be  vastly  more  remote ;  for,  of 
two  stars  that  appear  close  together,  one  may  be  far 
beyond  the  other  in  the  depth  of  space.  The  light  of 
Sirius,  according  to  the  observation  of  Sir  John  Herschel, 
is  324  times  greater  than  that  of  a  star  of  the  sixth 
magnitude. 

Nothing  is  known  of  the  absolute  size  of  the  fixed 
stars ;  but  the  quantity  of  light  emitted  by  many  of 
them  shows  that  they  must  be  much  greater  than  the 
Sun.  Sirius  is  nearly  four  times  larger,  and  many  stars 
must  be  infinitely  larger  than  Sirius.  Sometimes  stars 
have  been  known  to  vanish  from  the  heavens,  and 
never  appear  afterwards  ;  the  lost  Pleiad  of  classical 
mythology  is  one  of  these.  The  last  disappearance  of 
a  star,  noted  by  astronomers,  was  in  1828.  Sometimes 
stars  have  all  at  once  appeared,  shone  with  a  bright 
light,  and  vanished.  A  remarkable  instance  of  this 
occurred  in  the  year  125,  which  is  said  to  have  in- 
duced Hipparchus  to  form  the  first  catalogue  of  stars. 
Another  star  appeared  near  the  constellation  of  the 
Eagle  in  389,  and  vanished,  after  remaining  for  three 
weeks  as  bright  as  Venus.  On  the  10th  of  October, 
1604,  a  brilliant  star  burst  forth  in  the  constellation  of 
Serpentarius,  which  continued  visible  for  a  year.  A 
more  recent  case  occurred  in  1670,  when  a  new  star 
was  discovered  in  the  head  of  the  Swan,  which,  after 
becoming  invisible,  reappeared,  and  having  undergone 
many  variations  of  light,  vanished  after  two  years,  and 
has  never  since  been  seen. 


ASTRONOMY.  «•  43 

.n  1572,  a  star  was  discovered  in  Cassiopeia,  which 
rapidly  increased  in  brightness  till  it  even  surpassed 
that  of  Jupiter;  it  then  gradually  diminished  in  splen- 
dor, and  having  exhibited  all  the  variety  of  tints  that 
indicate  the  changes  of  combustion,  vanished  sixteen 
months  after  its  discovery,  without  altering  its  position. 
It  is  impossible  to  imagine  any  thing  more  tremendous 
than  a  conflagration  that  could  be  visible  at  such  a 
distance.  It  is,  however,  suspected  that  this  star  may 
be  periodical,  and  identical  with  those  which  appeared 
in  945  and  1264.  There  are,  probably,  many  stars 
which  alternately  vanish  and  reappear,  among  the 
innumerable  multitudes  that  spangle  the  heavens ;  the 
periods  of  thirteen  have  already  been  pretty  well 
ascertained. 

Of  these  the  most  remarkable  is  in  the  constellation 
of  the  Whale.  It  appears  about  twelve  times  in  eleven 
years,  and  is  of  variable  brightness,  sometimes  seem- 
ing like  a  star  of  the  second  magnitude ;  but  it  does 
not  always  attain  the  same  lustre,  nor  increase  and  di- 
minish by  the  same  degrees  ;  it  goes  through  a  com- 
plete revolution  of  brightness  and  obscurity  in  little 
less  than  three  days.  The  cause  of  the  variations  in 
most  of  the  periodical  stars  is  unknown,  but  it  is  con- 
jectured that  they  may  be  occasioned  by  the  revolution 
of  some  opaque  body  coming  between  us  and  them. 
Sir  John  Herschel  is  struck  with  the  high  degree  of 
4  activity  evinced  by  these  changes,  in  regions  where 
"  but  for  such  evidences  we  might  conclude  all  to  be 
lifeless." 

Many  thousands  of  stars  seem  to  be  only  brilliant 
points ;  but,  when  carefully  examined,  are  found  to  be, 


44  »  ASTRONOMY. 

in  reality,  systems  of  two  or  more  suns,  revolving 
round  each  other,  or  round  a  common  centre.  These 
double  and  multiple  stars  are  very  remote,  requiring 
the  most  powerful  telescopes  to  show  them  separately. 
The  motions  of  revolution  of  many  of  these  stars 
round  a  common  centre  have  been  ascertained,  and 
their  periods  determined  with  considerable  accuracy. 
Some  have  accomplished  a  whole  revolution,  since 
their  discovery.  One  of  these  stars  revolves  round 
the  other  in  1600  years,  another  in  58.  It  sometimes 
happens  that  the  edge  of  the  orbit  of  a  star  is  presented 
towards  the  Earth  ;  it  then  seems  to  move  in  a  straight 
line,  and  to  oscillate  on  each  side  of  its  primary.  There 
are  also  quadruple  stars,  and  even  assemblages  of  five 
and  six,  revolving  round  each  other. 

Besides  revolutions  around  one  another,  some  of  the 
binary  systems  are  carried  forward  in  space,  by  a  mo- 
tion common  to  both  stars,  toward  some  unknown  point 
in  the  firmament.  Two  stars  in  the  Swan,  which  are 
nearly  equal,  and  have  remained  at  the  same  distance 
from  each  other  for  above  fifty  years,  have  changed 
their  place  in  the  heavens,  during  that  period,  between 
four  and  five  minutes,  with  a  motion  which  for  ages 
must  appear  uniform  and  rectilinear,  because,  even  if 
the  path  be  curved,  so  small  a  portion  of  it  must  appear 
a  straight  line  to  us.  The  single  stars,  also,  have 
proper  motions ;  our  own  Sun  is  supposed  to  be 
moving  towards  a  certain  point  in  the  heavens. 

Though  the  absolute  distance  of  the  fixed  stars  is 
still  unknown,  a  limit  has  been  found  within  which, 
probably,  some  of  them  come.  It  was  natural  to  sup- 
pose that,  in  general,  the  large  stars  are  nearer  to  the 


ASTRONOMY.  45 

Earth  than  the  small  ones ;  but  there  is  now  reason  to 
believe  that  some  stars,  though  by  no  means  so  brilliant, 
are  nearer  to  us  than  others  which  shine  with  greater 
splendor.  This  is  inferred  from  the  comparative  ve- 
locity of  their  movements.  In  consequence  of  the  pro- 
gressive motion  of  our  Sun,  and  its  planets,  all  the  fixed 
stars  have  an  apparent  motion,  which  tends  ultimately 
to  mix  the  stars  of  the  different  constellations ;  but 
none  that  we  know  of  moves  so  rapidly  as  No.  61  of 
the  Swan  ;  and  on  that  account  it  is  reckoned  to  be 
nearer  to  us  than  any  other,  —  for  an  object  which  we 
are  passing  by  seems  to  move  more  quickly,  the 
nearer  we  are  to  it. 

This  circumstance  induced  Messrs.  Arago  and  Mat- 
thieu  to  endeavor  to  determine  its  annual  parallax; 
that  is,  to  ascertain  what  magnitude  the  diameter  of  the 
Earth's  orbit  would  have,  as  seen  from  the  star.  They 
found,  by  observation,  that  the  orbit's  diameter  of 
190  millions  of  miles  would  be  seen  from  the  star 
under  an  angle  of  only  half  a  second ;  whence  this 
star  must  be  at  the  distance  of  420  millions  of  times 
190  millions  of  miles  from  the  earth!  —  a  distance 
which  light,  flying  at  the  rate  of  190,000  miles  in  a 
second,  would  not  pass  over  in  less  than  six  years. 
This  is  the  smallest  distance  at  which  the  star  can  be : 
how  much  greater  its  real  distance  is,  it  is  impossible  to 
say.  The  apparent  motion  of  five  seconds  annually, 
which  this  star  has,  seems  to  us  extremely  small ;  but  at 
that  distance  an  angle  of  one  second  corresponds  to 
24  millions  of  millions  of  miles;  consequently,  the 
annual  motion  of  this  star  is  120  millions  of  millions 
of  miles  ;  and  yet,  as  M.  Arago  observes,  we  call  it  a 
fxed  star! 


The  doable  stars  are  of  various  hoes,  tat  they  most 
frequently  exhibit  the  contrasted  colors.  The  large 
star  is  generally  yellow,  orange,  or  red  :  and  die  snail 
star  Uoe,  parpfe,  or  green.  Sometimes  a  white  star  is 
combined  with  a  bine  or  purple  one,  and  more  rarely 
a  red  and  white  one  are  united.  In  many  cases,  these 
appearances  arise  from  the  influence  of  contrast  on  oar 
judgment  of  colors.  For  example,  in  observing  a 
double  star,  when  the  large  one  is  a  full  ruby  red,  or 
almost  blood  color,  and  the  small  one  a  fine  green,  the 
latter  loses  its  color  when  the  former  is  hidden  by  the 
cross-wires  of  the  telescope.  But  there  is  a  vast  num- 
ber of  instances  where  the  colors  are  too  strongly 
to  be  merely  imaginary.  Sir  John  Herschel 
a  very  remarkable  fact,  that,  although  red 
stars  are  common  enough,  no  example  of  a  solitary 
Woe,  green,  or  purple  one  has  been  produced. 

The  stars  are  Tery  irregolariy  scattered  over  the 
firmament.  In  some  places,  they  are  crowded  to- 
gether, in  others  thinly  dispersed.  A  few  groups,  more 
closely  condensed,  form  very  beautiful  objects  even  to 
the  naked  eye,  —  of  which  the  Pleiades,  and  the  constel- 
lation Berenice's  Hair,  are  the  most  striking  examples. 
Bat  the  greater  number  of  these  clusters  of  stars  appear, 
to  iinaiiiili  il  roan,  like  thin  white  clouds,  or  vapor ; 
such  B  the  Milky  Way,  which,  as  Sir  William  Herschel 
has  proved,  derives  its  laig|jiiM«  from  the  diffused 
fight  of  the  myriads  of  stars  that  form  it.  Most  of 
these  stars  appear  to  be  extremely  snail,  on  BLLUSB* 
of  their  enormous  distances. 

This  wignbr  portion  of  the  heavens,  consntnting 
part  of  oar  firmament,  consists  of  an  extensive  mass 


ASTRONOMY. 


of  stars,  the  thickness  of  which  is  small  compared  to  its 
length  and  breadth  ;  the  Earth  is  placed  at  the  point 
where  it  divides  into  two  branches,  and  it  appears  to  be 
much  more  splendid  in  the  southern  hemisphere  than 
in  the  northern.  Sir  John  Herschel  says,  "  The  gen- 
eral aspect  of  the  southern  circumpolar  regions,  inc.ud- 
ing  in  that  expression  60  or  70  degrees  of  south  polar 
distance,  is  in  a  high  degree  rich  and  magnificent, 
owing  to  the  superior  brilliancy  and  large  development 
of  the  Milky  May,  which,  from  the  constellation  of 
Orion  to  that  of  Antinous,  is  a  blaze  of  light,  strangely 
interrupted,  however,  with  vacant  and  entirely  starless 
patches,  especially  in  Scorpio,  near  Alpha  Centauri 
and  the  Cross ;  while  to  the  north  it  fades  away  pale  and 
dim,  and  is,  in  comparison,  hardly  traceable.  I  tliink 
it  impossible  to  view  this  splendid  zone,  with  the  aston- 
ishingly rich  and  evenly-distributed  fringe  of  stars  of 
the  third  and  fourth  magnitude,  which  forms  a  broad 
skirt  to  its  southern  border,  like  a  vast  curtain,  without 
an  impression,  amounting  almost  to  conviction,  that  the 
Milky  Way  is  not  a  mere  stratum,  but  annular  ;  or,  at 
least,  that  our  system  is  placed  within  one  of  the  poorer 
or  almost  vacant  parts  of  its  general  mass  !  The  clus- 
ter of  which  our  Sun  is  a  member,  and  which  includes 
the  Milky  Way  and  all  the  stars  that  adorn  our  sky, 
must  be  of  enormous  extent,  since  the  Sun  is  more  than 
20  millions  of  millions  of  miles  from  the  nearest  of 
them  ;  and  the  other  stars,  though  apparently  so  close 
together,  are  probably  separated  from  one  another  by 
distances  equally  great." 


48  ASTRONOMY. 


METEORITES. 

If  such  remote  bodies  as  the  fixed  stars  shone  by 
reflected  light,  we  should  be  unconscious  of  their  exist- 
ence. Each  star  must  then  be  a  sun,  and  may  be 
presumed  to  have  its  system  of  planets,  satellites,  and 
comets,  like  our  own ;  and  for  aught  we  know,  myriads 
of  bodies  may  be  wandering  in  space  unseen  by  us,  of 
whose  nature  we  can  form  no  idea,  and  still  less  of  the 
part  they  perform  in  the  economy  of  the  universe. 
Even  in  our  own  system,  at  its  farthest  limits,  minute 
bodies  may  be  revolving  like  the  new  planets,  which 
are  so  small  that  their  masses  have  hitherto  been  inap- 
preciable, and  there  may  be  many  still  smaller. 

Nor  is  this  an  unwarranted  supposition  ;  many  such 
do  come  within  the  sphere  of  the  Earth's  attraction,  are 
ignited  by  the  velocity  with  which  they  pass  through 
the  atmosphere,  and  are  precipitated  with  great  violence 
on  the  Earth.  The  fall  of  meteoric  stones  is  much 
more  frequent  than  is  generally  believed.  Hardly  a 
year  passes  without  some  instances  occurring;  and  if 
it  be  considered  that  only  a  small  part  of  the  Earth  is 
inhabited,  it  may  be  presumed  that  numbers  fall  in 
the  ocean,  or  on  the  unoccupied  part  of  the  land, 
unseen  by  man.  They  are  sometimes  of  great  mag- 
nitude ;  the  bulk  of  several  has  exceeded  that  of  the 
planet  Ceres,  which  is  about  70  miles  in  diameter. 
One,  which  passed  within  25  miles  of  the  Earth,  was 
estimated  to  weigh  about  600,000  tons,  and  to  move  with 
a  velocity  of  about  20  miles  in  a  second ;  a  fragment 
of  it  alone  reached  the  ground.  The  obliquity  of  the 
descent  of  meteorites,  the  peculiar  substances  of  which 


ASTRONOMY.  49 

they  are  composed,  and  the  explosion  accompanying 
their  fall,  show  that  they  are  foreign  to  our  system. 

Luminous  spots  have  occasionally  appeared  on  the 
dark  part  of  the  moon.  These  have  been  ascribed  to 
the  light  arising  from  the  eruption  of  volcanoes ;  whence 
it  has  been  supposed  that  meteorites  have  been  pro- 
jected from  the  moon  by  the  force  of  volcanic  erup- 
tion. It  has  even  been  computed  that  if  a  stone  were 
projected  from  the  moon  in  a  vertical  line,  with  an  initial 
velocity  of  10,992  feet  in  a  second,  (more  than  fo^ir 
times  the  velocity  of  a  cannon-ball,)  instead  of  falling 
back  to  the  moon  by  the  attraction  of  gravity,  it  would 
come  within  the  sphere  of  the  Earth's  attraction,  and 
revolve  about  it  like  a  satellite.  These  bodies,  impelled 
either  by  the  direction  of  the  primitive  impulse  or  by 
the  disturbing  action  of  the  Sun,  might  ultimately  pene- 
trate the  Earth's  atmosphere  and  arrive  at  its  surface  ; 
but  it  is  much  more  probable  that  they  are  asteroids 
revolving  about  the  Sun,  and  diverted  from  their  course 
by  some  disturbing  force  ;  at  all  events,  they  must  have 
a  common  origin,  from  the  uniformity  of  their  chemical 
composition. 

AEROLITES. 

Shooting  stars  and  meteors  differ  from  aerolites  in 
several  respects.  Aerolites  burst  from  the  clear  azure 
sky,  and,  darting  along  the  heavens,  are  extinguished 
without  leaving  any  residuum  except  a  vapor-like 
smoke,  and  generally  without  noise.  Calculations  have 
shown  them  to  be  very  high  in  the  atmosphere  —  some- 
times even  beyond  its  supposed  limit ;  and  the  direction 
of  their  motion  is,  for  the  most  part,  opposite  to  the 

D  XIII. — 5 


50  ASTRONOMY. 

motion  of  the  earth  in  its  orbit.  The  astonishing  mul- 
titudes of  shooting  stars  and  fire-balls  that  have  appeared 
within  these  few  years,  at  stated  periods,  over  the 
American  continent,  and  other  parts  of  the  globe,  war- 
rant the  conclusion  that  there  is  either  a  nebula,  or  that 
there  are  myriads  of -bodies  revolving  round  the  Sun, 
which  become  visible  only  when  inflamed  by  entering 
our  atmosphere. 

One  of  these  nebulae,  or  groups,  seems  to  approach 
cl{>se  to  the  Earth,  in  its  annual  revolution,  on  the  12th 
or  13th  of  Novembet.  On  the  morning  of  the  12th 
of  November,  1799,  thousands  of  shooting  stars,  mixed 
with  large  meteors,  illuminated  the  heavens,  for  many 
hours,  over  the  whole  continent  of  America,  from  Bra- 
zil to  Labrador ;  they  were  observed  even  in  Green- 
land and  Germany.  Meteoric  showers  were  seen  off 
the  coast  of  Spain,  and  in  Ohio,  on  the  morning  of  the 
13lh  of  November,  1831.  In  1832,  during  many  hours 
of  the  morning  of  the  13th  of  November,  prodigious 
multitudes  of  shooting  stars  and  meteors  fell  at  Mocha, 
on  the  Red  Sea,  in  the  Atlantic,  in  Switzerland. and 
England. 

But  by  far  the  most  splendid  meteoric  shower  on 
record  was  in  1833.  It  began  at  nine  o'clock  in  the 
evening  of  the  12th  of  November,  and  continued  till 
sunrise  the  next  morning.  It  extended  from  the  great 
lakes  of  Canada,  southward,  to  Jamaica,  and  from  the 
61st  degree  of  longitude  in  the  Atlantic,  westerly,  to  the 
100th  degree  in  Central  Mexico.  Shooting  stars  and 
meteors,  of  the  apparent  size  of  Venus,  Jupiter,  and 
even  the  full  moon,  darted  in  myriads  towards  the 
horizon,  as  if  all  the  stars  in  the  heavens  had  started 


ASTRONOMY.  51 

from  their  spheres.  Those  who  witnessed  this  grand 
spectacle  were  surprised  to  see  that  every  one  of  these 
luminous  bodies,  without  exception,  moved  in  lines 
which  converged  to  one  point  in  the  heavens.  None 
of  them  started  from  that  point ;  but  their  paths,  when 
traced  backward,  met  in  it  like  rays  hi  a  focus,  and  the 
manner  of  their  fall  showed  that  they  descended  from 
it  in  nearly  parallel  straight  lines.  The  most  extraor- 
dinary part  of  the  phenomenon  is,  that  this  radiating 
point  was  observed  to  remain  stationary,  in  the  constel- 
lation Leo,  for  more  than  two  hours  and  a  half,  —  whick 
proves  the  source  of  the  meteoric  shower  to  be  alto- 
gether independent  of  the  Earth's  rotation.  Other  ob- 
servations showed  it  to  be  far  above  the  atmosphere. 

As  all  the  circumstances  of  the  phenomenon  were 
similar,  on  the  same  day,  and  during  the  same  hours,  hi 
1832,  and  as  extraordinary  flights  of  shooting  stars 
were  seen  at  many  places,  both  in  Europe  and  Amer- 
ica, on  the  13th  of  November,  1834,  and  the  two  fol- 
lowing years,  proceeding  also  from  a  fixed  point  in  the 
constellation  Leo,  it  has  been  conjectured,  with  much 
apparent  probability,  that  this  nebula,  or  group  of  bodies, 
performs  its  revolution  round  the  Sun  in  a  period  of 
about  182  days,  in  an  elliptical  orbit,  and  that  its  great- 
est distance  from  the  Sun  is  about  95,000,000  of  miles, 
which  brings  it  in  contact  with  the  Earth's  atmosphere. 

NEBULOUS  STARS. 

We  are  now  about  to  introduce  to  the  reader's  notice 
the  most  wonderful  discovery  ever  made  in  the  science 
of  astronomy,  —  namely,  a  planetary  system  in  the  pro- 
cess of  formation,  or  a  chaos  of  matter  gradually  gath- 


52  ASTRONOMY. 


ering  into  the  shape  of  suns  with  their  attendant  worlds ! 
Certain  dim  spots,  or  diffused  luminous  patches,  in  the 
heavens,  have  long  been  known  to  astronomers  by  the 
name  of  nebula ;  but  their  phenomena  were  looked 
upon  as  inexplicable,  and  regarded  as  barren  marvels, 
until  Sir  William  Herscnel  completely  surveyed  them 
all,  studied  their  curious  relations,  and  formally  pre- 
sented his  views  concerning  their  probable  nature. 
These  nebulae  are  of  two  sorts,  planetary  and  stellar. 
In  the  former,  we  behold  a  starlike  body,  surrounded 
with  a  luminous  atmosphere,  which  the  strongest  tel- 
escopes are  unable  to  resolve  into  separate  stars,  but 
which,  under  every  magnifying  power,  still  continue 
to  present  the  appearance  of  a  vague  film. 

Sir  John  Herschel  says  of  one  of  them,  in  Orion's 
sword,  "  I  know  not  how  to  describe  it  better  than  by 
comparing  it  with  the  cu/dling  of  a  liquid,  or  to  a  sur- 
face strewed  over  with  flocks  of  wool,  or  to  the  break- 
ing up  of  a  mackerel  sky,  when  the  clouds  begin  to 
assume  a  linear  appearance.  It  is  not  very  unlike  the 


ASTRONOMY.  53 

mottling  of  the  sun's  disk,  only  the  grain  is  much 
coarser  and  the  intervals  darker,  and  \\\ejlocculi,  instead 
of  being  round,  are  drawn  into  little  wisps.  They  pre- 
sent, however,  no  appearance  of  being  composed  of 
stars,  and  their  aspect  is  altogether  different  from  those 
of  resolvable  nebulae.  In  these  we  fancy,  by  glimpses, 
that  we  see  stars,  or  that,  could  we  strain  our  sight  a 
little  more,  we  should  see  them  ;  but  the  former  sug- 
gest no  idea  of  stars,  but  rather  of  something  quite  dis- 
tinct from  them. 

"  In  reference  to  the  great  nebula  in  the  girdle  of 
Andromeda,  there  are  grounds  for  a  similar  conclusion. 
So  that  we  have  this  novel  and  most  singular  matter 
not  only  surrounding  stars,  and  enveloping  them  as  an 
immense  chevelure,  but  existing  also  isolated,  and  in 
various  conditions,  from  the  shape  of  perfect  diffusion, 
to  that  where,  as  in  Andromeda,  it  shows  a  central 
nipple,  or  an  apparent  point  of  condensation.  It  is, 
perhaps,  in  its  separate  and  independent  form  that  it 
fills  us  with  most  astonishment.  The  profusion  with 
\vhich  it  is  distributed,  in  this  form,  in  both  hemispheres, 
and,  indeed,  through  all  the  heavens,  would  imply  that 
it  fulfils,  or  is  pressing  to  fulfil,  some  important  func- 
tion in  the  material  economy." 

This  strange  fluid,  a  self-luminous,  phosphorescent, 
material  substance,  exists  in  a  great  variety  of  forms, 
but  generally  in  a  globular  shape,  and  in  all  varieties  of 
density.  Some  of  the  masses  are  only  a  thin  milky 
patch,  of  equal  tenuity  in  every  part ;  in  others,  there 
is  a  slight  condensation  toward  the  centre  :  this  con- 
densation augments,  till,  at  length,  we  behold  a  distinctly- 
formed  star,  surrounded  by  a  nebulous  atmosphere. 
5* 


M  ASTRONOMY. 

The  inference  is  irresistible,  that  they  are  masses  of 
chaotic  matter,  in  a  highly  diluted  or  gaseous  state, 
gradually  subsiding,  by  the  mutual  gravitation  of  their 
particles,  into  stars  and  sidereal  systems.  This  is  the 
hypothesis  of  Laplace  with  regard  to  the  origin  of  the 
solar  system,  which  he  conceived  to  be  formed  by  the 
successive  condensations  of  a  nebula  whose  primeval 
rotation  is  still  maintained  in  the  rotation  and  revolution 
of  the  Sun,  and  all  the  bodies  of  the  solar  system,  in  the 
same  direction.  Even  at  this  day,  there  is  presumptive 
evidence,  in  the  structure  and  internal  heat  of  the  Earth, 
of  its  having  been  at  one  period  in  a  gaseous  state, 
from  an  intensely  high  temperature. 

The  question  will  naturally  occur  here,  How  can 
such  stars  as  we  see  come  out  of  these  nebulous 
masses  ?  and  can  any  star,  thus  produced,  resemble  in 
character  the  known  individuals  of  our  heavens  ?  To 
a  certain  extent  this  inquiry  has  been  answered,  in- 
geniously and  satisfactorily.  It  is  manifest  that  the 
orbs  arising  out  of  a  nebula  would  be  subject  to  a 
motion  of  rotation  on  an  axis,  as  the  Sun  is,  and,  in  all 
probability,  the  fixed  stars  are.  The  confluence  of 
particles  toward  a  centre  of  attraction  would,  in  gen- 
eral, if  not  universally,  produce  a  whirlpool,  of  which 
an  illustration  is  extant  in  the  confluence  of  almost  all 
differently-flowing  streams.  A  rotary  motion  once 
communicated,  its  velocity  would  increase  with  the 
process  of  condensation.  The  resulting  orbs,  then, 
would  rotate  ;  and  as  the  circumstances  of  their  origin 
would  vary,  they  would  rotate  in  varying  times.  The 
phenomenon  of  the  double  stars  is  also  explained  here. 
The  whirlpool  motion  of  the  original  nebula  would  in- 


ASTRONOMY.  55 

evitably  cause  an  orbitual  revolution  of  binary  and  more 
complex  systems.  A  diffused  nebulosity  is  sometimes 
seen  broken  up  into  two  or  more  round  nebulae,  yet 
hardly  separated.  If  these  individual  masses  rotate, 
or  are  like  whirlpools,  they  must  act  on  each  other  as 
wheels ;  the  result  may  be  illustrated  by  a  very  fa- 
miliar example.  AValk  along  the  side  of  a  river,  and 
notice  the  little  moving  eddies  caused  in  such  multi- 
tudes by  the  interference  of  currents  from  the  unequal 
sides  of  the  stream ;  follow  these  small  eddies  for  a 
moment,  and  observe  how,  on  being  whirled  down  the 
stream,  they  come  into  contact  or  proximity  to  each 
other ;  that  instant  they  form,  a  system,  the  one  revolv- 
ing round  the  other,  or  rather  both  revolving  round 
some  intermediate  point. 

The  Sun,  and,  probably,  the  other  orbs,  are  attended 
by  planets ;  and  it  is,  perhaps,  the  most  interesting  part 
of  the  whole  speculation,  to  follow  Laplace  in  his  ac- 
count of  the  gradual  formation  of  these  minute  circum- 
stellar  bodies  from  the  bosom  of  the  condensing  nebula. 
In  any  given  state  of  the  rotating  mass,  the  outer  por- 
tion, or  ring,  is  in  the  condition  of  having  its  centrif- 
ugal force  exactly  balanced  by  its  gravity.  The  rota- 
tion increasing  in  rapidity  in  consequence  of  the  pro- 
gressing condensation,  the  mass  of  the  nebula  will 
abandon  this  outer  ring  of 'matter,  which  may  after- 
wards continue  to  circulate  about  the  star.  Imagina- 
tion may  conceive  several  zones  of  vapor  thus  succes- 
sively abandoned,  and  moving,  with  velocities  corre- 
sponding to  their  position,  around  the  Sun,  or  central 
nebulous  mass.  The  particles  of  such  rings  might 
condense  into  a  solid  or  liquid  substance ;  but,  unless  the 


56  ASTRONOMY. 

formations  were  originally  uniform  in  all  their  parts,  — 
an  iVnprobable  hypothesis,  —  they  would  not  condense 
as  rings.  We  have,  in  fact,  only  one  example  of  such 
a  circumstance  in  the  rings  of  Saturn,  —  a  phenomenon 
altogether  invaluable  in  illustration  of  the  primary  con- 
dition of  our  system.  In  most  cases,  these  zones  would 
divide,  and  form  several  masses,  circulating  around  the 
Sun.  The  same  process,  in  the  mean  time,  would  be 
going  on  with  regard  to  the  planets,  in  the  formation  of 
their  satellites. 

Distinct  evidences  of  the  originally  nebulous  state  of 
the  solar  system  are  not  wanting.  There  is  a  phe- 
nomenon called  the  zodiacal  light,  which  may  be  seen 
in  the  twilight  of  morning  and  evening,  in  the  neigh- 
borhood of  the  Sun,  in  the  shape  of  a  pyramid,  or  cone, 
rising  above  the  horizon,  and  considerably  inclined  on 
one  side.  It  appears  to  extend  beyond  the  orbit  of 
Venus,  and  is  regarded  as  a  portion  of  the  original 
nebular  mass  of  our  system  not  yet  condensed.  The 
comets,  moreover,  are  evidently  nebulous  bodies,  and 
most  of  them  are  strangers  to  our  system,  or  rather, 
fortuitous  visitants.  This  fact  merely  indicates  that  we 
must  seek  their  origin  in  the  external  spaces,  and  we 
find  it  in  those  masses  of  nebulous  fluid  with  which  they 
are  intimately  connected  by  constitution,  and  whose 
formerly  questionable  existence  they  render  visible  and 
almost  tangible.  How  interesting  the  change  which 
passes  over  the  whole  aspect  of  these  wandering 
bodies,  when  viewed  in  their  true  position,  not  as 
anomalies,  not  as  monstrous  and  disturbing  intruders 
into  a  system  with  which  they  are  not  connected  by 
any  harmonizing  ties,  but  as  outposts  of  a  mighty  sys- 


ASTRONOMY.  57 

temt  which  vastly  extend  our  notions  of  that  amount  of 
formless  matter  existing  among  the  stellar  intervals, 
and  which  are  themselves  in  progress  toward  a  more 
perfect  organization  ! 

In  illustration  of  the  process  of  the  formation  of  stars 
and  systems  from  nebulse,  the  following  cut  speaks 
to  the  eye,  and  is  more  valuable  than  pages  of  descrip- 
tion. Each  figure  in  this  plate  is  the  representation, 


Stars  and  Systems  forming  from  J^'elndte. 

not  of  an  individual,  but  of  an  extensive  class;  and  it 
would  seem  that  a  series  so  well  marked,  so  striking 
in  its  aspects,  must  indicate  the  presence  and  influence 
of  a  great  law.  From  absolute  vagueness  to  distinct 
structure,  and  then  on  to  the  formation  of  a  defined 
central  nucleus,  the  nebula  seems  growing  under  our 
eye  !  "  We  look,"  says  Laplace,  "  among  these  ob- 
jects as  among  the  trees* of  a  forest;  their  change,  in 
the  duration  of  a  glance,  is  undiscoverable :  yet  we 
perceive  that  these  are  plants  in  all  different  stages ; 
we  see  that  these  stages  are  probably  related  to  each 
other  in  the  order  of  time,  and  we  are  irresistibly  led 


58  ASTRONOMY. 

to  the  conclusion  that  the  vegetable  world,  in  the  one 
case,  and  the  sidereal  world  in  the  other,  exhibit,  at  one 
instant,  a  succession  of  changes  requiring  time,  which 
the  life  of  man,  or  the  duration  of  the  solar  system,  may 
not  be  sufficient  to  trace  out  in  individual  instances." 

There  is  a  creature  called  the  ephemeron,  whose 
life  is  limited  within  a  mere  point  of  time  ;  in  a  single 
day  it  dances  out  its  existence  in  the  sunbeam.  That 
creature  lives  in  the  presence  of  all  the  phenomena  of 
vegetable  growth ;  it  may  see  trees,  it  may  see  flow- 
ers ;  but  how  could  it,  or  its  generations,  actually  ob- 
serve their  progressive  development  ?  In  relation  to 
the  nebulse,  man  is  but  an  ephemeron.  Fifty  lives 
succeeding  each  other,  and  of  a  length  to  which  indi- 
viduals often  attain,  would  reach  backward  beyond  the 
recorded  commencement  of  his  race  ;  and,  in  the  muta- 
bility of  things,  fifty  more  may  close  its  career.  Thus 
no  more  than  what  one  hundred  ephemera  can  see  of  the 
progress  upward  of  the  majestic  pine,  will  man,  perhaps, 
ever  actually  behold  of  the  changes  of  the  nebula?. 

Yet,  after  all,  where  is  the  intrinsic  difference  be- 
*ween  the  formation  of  a  system  of  worlds,  and  the 
growth  and  progress  of  the  humblest  leaf  from  its  seed 
to  its  intricate  and  most  beautiful  organization  ?  That 
which  bewilders  us  is  not  any  intrinsic  difficulty  or 
disparity,  but  a  consideration  springing  from  our  own 
fleeting  condition.  We  are  not  rendered  incredulous 
by  the  nature,  but  overwhelmed  by  the  magnitude,  of 
these  creations ;  our  minds  will  not  stretch  out  to  em- 
brace the  periods  of  this  stupendous  change.  But  time 
is  illimitable,  and  we  are  speaking  of  the  operations,  and 
tracing  the  footsteps,  of  a  Being  who  is  above  all  time  ; 
we  are  contemplating  the  energies  of  that  almighty 


ASTRONOMY.  59 

mind,  to  whose  infinite  capacity  a  day  is  as  a  thousand 
years,  and  the  lifetime  of  the  entire  human  race  but  as 
the  moment  which  dies  with  the  tick  of  the  clock  that 
marks  it  —  which  is  heard  and  strafghtway  passes. 

THE  FIRMAMENTAL   SYSTEMS. 

Notwithstanding  the  amazing  extent  of  the  worlds, 
and  systems  of  worlds,  we  have  described,  they  do  not 
constitute  the  whole  universe,  but  only  a  very  small 
part  of  it.  Countless  firmaments,  or  clusters  of  stars, 
distinct  from  ours,  and  at  an  immense  distance  from  it, 
exist,  sustaining  an  independent  position,  as  individual 
constituents  of  creation.  We  have  already  carried  our 
researches  into  what  seemed  the  infinity  of  space  ;  but 
we  must  now  go  forth  into  far  deeper  infinity  among 
these  firmaments,  and  ascertain  their  character. 

In  the  intervals  between  the  stars  of  our  own  system, 
and  at  an  immense  distance  beyond  them  in  the  depths 
of  space,  many  clusters  of  stars  may  be  seen,  like 
white  clouds,  or  round,  comets  without  tails.  When 
examined  with  proper  instruments,  they  convey  the 
idea  of  a  globular  space,  insulated  in  the  heavens,  and 
filled  full  of  stars,  constituting  a  family,  or  society,  apart 
from  the  rest,  subject  only  to  its  own  internal  laws. 
The  number  of  these  masses  is  very  great.  In  the 
northern  hemisphere,  after  making  all  allowances,  those 
whose  places  are  fixed  cannot  be  fewer  than  1000  or 
2000 ;  and  we  may  form  some  idea  how  plentifully 
they  are  distributed,  by  recollecting  that  this  is  at 
least  equal  to  the  whole  number  of  stars  which  the 
naked  eye  beholds  at  once  on  any  ordinary  night. 


60 


ASTRO  NOMF. 


Various  Forms  of  Nebula. 

To  attempt  to  count  the  stars  in  one  of  these  clus- 
ters, would  be  a  vain  task ;  they  are  to  be  reckoned  not 
by  hundreds,  but  by  thousands.  On  a  rough  computa- 
tion, it  appears  that  many  of  them  must  contain  10 
or  20,000  stars,  compacted  and  wedged  together  in  a 
globular  space,  whose  area  is  not  more  than  a  tenth 
part  of  that  covered  by  the  moon;  so  that  its  centre, 


ASTRONOMY.  61 

where  the  stars  are  seen  condensed,  is  one  blaze  of 
light.  If,  as  we  have  every  reason  to  believe,  each  of 
these  stars  be  a  sun,  and  if  they  be  separated  by  inter- 
vals equal  to  that  which  separates  our  Sun  from  the 
nearest  fixed  star,  the  distance  which  renders  the 
whole  cluster  barely  visible  to  the  naked. eye,  must  be 
so  great,  that  the  existence  of  this  splendid  assemblage 
can  only  be  known  to  us  by  light  which  must  have  left 
it  a  thousand  years  ago  ! 

These  clusters  have  a  variety  of  shapes  —  some  of 
them  most  singular  and  fantastic.  In  many  of  them, 
individual  stars  are  distinctly  defined.  As  they  become 
more  remote,  the  intervals  between  the  stars  dimmish, 
and  the  light  grows  fainter.  In  their  faintest  stellar 
aspect,  they  may  be  compared  to  a  handful  of  fine, 
sparkling  sand,  or,  as  it  is  aptly  termed,  star-dust 
Beyond  this  we  see  no  stars,  but  only  a  streak,  or  patch, 
of  milky  light.  Vast  multitudes  of  these  are  so  faint  as 
to  be  with  difficulty  discerned  at  all,  till  they  have  been 
for  some  time  in  the  field  of  the  telescope,  or  are  just 
about  to  quit  it.  Occasionally,  they  are  so  vague,  that 
the  eye  is  conscious  of  something,  without  being  able 
to  define  what  it  is ;  but  the  unchangeableness  of  its 
position  proves  that  it  is  a  real  object. 

The  central  cluster  of  stars,  in  the  preceding  cut, 
is  a  good  specimen-object,  as  it  is  a  representative, 
or  type,  of  a  very  large  class.  Notwithstanding  the 
partial  irregularity  of  its  outline,  it  seems  almost  a 
spherical  mass,  in  which,  with  a  degree  of  greater 
compression  toward  the  centre,  the  stars  are  pretty 
equally  and  regularly  diffused,  so  that,  to  the  inhabitants 
01  worlds  near  its  central  regions,  its  sky  would  spangle 
xra. — 6 


62  ASTRONOMY. 

uniformly  all  around,  and  present  no  phenomenon  like 
the  Milky  Way,  in  ours.  Others  of  the  spherical  clus- 
ters show  a  much  greater  compression  about  the  cen- 
tre —  a  circumstance  which  would  manifestly  augment 
the  proportionate  number  of  orbs  of  the  first  magni- 
tude in  view  of  those  living  within  the  compressed 
portion,  and  thus  render  their  visible  heavens  incon- 
ceivably brilliant.  Firmaments,  however,  are  by  no 
means  confined  to  the  spherical  form,  as  we  have 
already  remarked.  In  the  southern  hemisphere,  a 
phenomenon,  known  by  the  name  of  the  Magellanic 
Clouds,  long  excited  the  wonder  of  all  beholders 
These  clouds  have  been  found  to  be  immense  nebulae, 
or  firmaments,  of  a  singular  shape.  The  following  is 
a  representation  of  one  of  them. 


This  nebula,  according  to  the  description  of  Sir  John 
Herschel,  who  spent  some  time  at  the  Cape  of  Good 
Hope,  in  astronomical  researches,  "  is  a  congeries  of 
clusters  of  irregular  form,  globular  clusters,  and  nebulse 
of  various  magnitudes  and  degrees  of  condensation, 


ASTRONOMY.  63 

among  which  is  interspersed  a  large  portion  of  irresol- 
vable nebulae,  which  may  be,  and  probably  is,  star-dust, 
but  which  the  powers  of  the  twenty-feet  telescope  show 
only  as  a  general  illumination  of  the  field  of  view,  form- 
ing a  bright  ground,  on  which  the  other  objects  are 
scattered.  Some  of  the  objects  in  it  are  of  very  singu- 
lar and  incomprehensible  forms  —  the  chief  one  espe- 
cially, which  consists  of  a  number  of  loops,  united  in  a 
kind  of  unclear  centre  or  knot,  like  a  bunch  of  ribbons 
disposed  in  what  is  called  a  true-love  knot  There  is 
no  part  of  the  heavens  where  so  many  nebulae  and 
clusters  are  crowded  into  so  small  a  space  as  this 
cloud!" 

But  it  is  when  we  arrive  among  the  almost  bewil- 
dering multitudes  of  unresolved  systems,  that  we  are 
most  forcibly  struck  by  the  variations  of  their  fantastic 
shapes.  The  unresolved  clusters  being  at  depths  much 
profounder  than  the  sites  of  the  others,  the  sphere  ap- 
propriated to  them  is,  of  course,  of  larger  radius,  and 
far  more  capacious,  so  that  there  is  room  for  greater 
numbers,  and  also  a  more  wonderful  display  of  variety. 
The  accompanying  sketch  exhibits  a  few  of  these 


64  ASTRONOMY. 

curious  shapes.  The  annular  form  sometimes  occurs ; 
one  fine  instance  of  it  is  in  the  constellation  of  the  Lyre. 
The  oblong  sharp  hoop,  represented  in  the  preceding 
cut,  is  probably  likewise  a  large  ring,  but  appearing 
sharp  in  consequence  of  its  oblique  position  with  regard 
to  us.  How  utterly  different  from  ours  must  be  the 
aspects  of  the  sky  to  the  inhabitants  of  such  a  firma- 
ment !  The  space  within  the  ring  is  nearly  a  blank, 
but  not  perfectly  so,  a  very  thin  mass  of  light  spreading 
over  it ;  so  that,  to  the  eye  of  a  spectator  placed  within 
the  space,  the  sides  will  appear  nearly  an  utter  blank, 
while  the  other  part  of  the  heavens  will  be  engirdled 
with  a  zone  of  the  most  dazzling  lustre. 

One  of  the  most  singularly-shaped  clusters  is  the 
large  object  in  the  preceding  page.  It  has  the  shape 
of  an  hour-glass,  or  dumb-bell ;  the  two  connected 
hemispheres,  as  well  as  the  connecting  isthmus,  being 
bright  and  beautiful,  manifesting  a  dense  collection  of 
stars  in  those  regions,  while  the  oval  is  completed  by 
two  spaces,  which  do  not  transmit  a  greater  quantity  of 
light,  nor  indicate  the  presence  of  a  larger  number  of 
stars,  than  the  comparatively  vacant  interior  of  the  ring 
above  described.  We  are  lost  in  mute  astonishment  at 
these  endless  diversities  of  character  and  form.  But 
in  the  apparent  aim  of  the  things  near  and  around  us, 
we  may  perhaps  discern  some  purpose  which  such 
variety  may  serve.  It  seems  the  object,  or  result,  of 
known  material  arrangements,  to  produce  every  variety 
of  creature;  and  perhaps  it  is  one  end  of  this  wonderful 
evolution  of  firmaments  of  all  orders,  magnitudes,  and 
forms,  that  there,  too,  the  law  of  variety  may  prevail, 


ASTK030MT.  65 

and  room  be  found  for  unfolding  the  whole  riches  of 
die  Almighty. 

Of  all  these  wonderful  exhibitions,  there  is  no  one 
more  singular  than  what  we  are  about  to  describe. 
Although  the  telescope  has  not  yet  enabled  us  to  lay 
out  the  plan  of  our  own  cluster  from  interior  surveys, 
it  exhibits  what  seems  to  be  its  very  picture  hung  up 
in  external  space.  The  accompanying  cut  represents 
a  nebula  resting  near  the  outermost  range  of  telescopic 


observation,  which  is  the  fac  simile  of  the  system  to 
which  we  belong !  A  double  representation  is  given, 
one  of  them  showing  it  in  a  broadside,  and  the  other  in 
an  edgewise  view.  It  has  its  surrounding  ring,  oftbe^^ 
precise  form  which  we  have  been  inclined  to  attribute 
to  our  Mflky  Way.  It  adds  much  to  the  interest  with 
which  we  contemplate  this  cluster,  that  the  inhabitants 
there  must  see  our  system  precisely  as  we  see  them? — 
namely,  sideways ;  so  that  we  behold  objects  of  the  same 
aspect  when  we  look  at  each  other.  Singular  affinity 
of  forms !  What  link,  what  far-reaching  sympathy, 
E  6* 


66  ASTRONOMY. 

can  connect  these  twin  masses,  —  that  unfathomed 
firmament  and  ours  !  What  virtue  is  there  in  a  shape 
so  fantastic,  that  it  should  be  thus  repeated  ?  — or  what 
is  the  august  law,  exerting  its  force  at  the  opposite  ex- 
tremities of  space,  which  has  caused  these  correspond- 
ing shapes  to  come  into  being  ? 

Struck  with  an  absorbing  and  most  natural  astonish- 
ment, we  soon  start  the  inquiry,  Wkat  are  these  clus- 
ters doing  1  What  is  their  internal  condition  ?  What 
are  their  mechanisms  ?  And  what  the  nature  and 
affections  of  the  bodies  which  compose  them  ?  Here 
we  approach  the  region  of  clouds  and  doubt ;  the  solid 
ground  of  fact  and  observation  begins  to  fail  us.  Yet 
we  are  not  without  warrant  in  pronouncing  that  these 
vast  masses  are  not  grouped  together  by  chance,  or  at 
random,  but  that  every  such  union  of  stars  indicates 
law  and  system.  The  only  light  we  find,  among  these 
immense  spaces,  is  a  welcome  gleam  of  evidence  that 
nature  there  is  also  uniform,  since  the  simpler  firma- 
ments manifest,  by  their  shapes,  the  prevalence  of  an 
internal  attractive  power.  Notwithstanding  the  fan- 
tastic forms  which  sometimes  occur,  the  round  or  glob- 
ular structure  is  the  general  or  favorite  one ;  and  in 
most  of  these  round  clusters  there  is  also  a  strongly- 
marked  increase  of  light  towards  the  centre,  much 
more  than  would  arise  from  the  circumstance  of  the 
eye  then  looking  through  the  deepest  part  of  the  group, 
and  thereby  seeing,  at  once,  the  greatest  number  of  its 
stars.  This  phenomenon  decidedly  indicates  compres- 
sion, in  a  greater  or  less  degree  ;  nor  is  it  confined  to 
masses  having  the  perfectly  spherical  figure.  "  There 
are  besides,"  says  Sir  William  Herschel,  "  additional 


ASTRONOMY.  67 

circumstances,  in  the  appearance  of  extended  clusters 
and  nebulae,  which  very  much  favor  the  idea  of  a  power 
lodged  in  the  brightest  part.  Although  the  form  of 
these  be  not  globular,  it  is  plainly  to  be  seen  that  there 
is  a  tendency  to  sphericity,  by  the  swell  of  the  dimen- 
sions the  nearer  we  draw  towards  the  most  luminous 
place  —  denoting,  as  it  were,  a  course,  or  tide,  of  stars, 
setting  towards  a  centre.  And  if  allegorical  expres- 
sions may  be  allowed,  it  should  seem  as  if  the  stars, 
thus  flocking  towards  the  seat  of  power,  were  stemmed 
by  the  crowd  of  those  already  assembled,  and  that 
while  some  of  them  are  successful  in  forcing  their  pred- 
ecessors sideways  out  of  their  places,  others  are  them- 
selves obliged  to  take  up  lateral  situations,  while  all  of 
them  seem  eagerly  to  strive  for  a  place  in  the  central 
swelling  and  generating  spherical  figure." 

Here  another  grand  field  for  contemplation  is  opened. 
Even  the  heavens  are  not  stable !  These  globular 
masses,  at  least,  are  in  process  of  growth,  are  ripening ; 
they  are  congregating  together  toward  that  nucleus 
round  which  a  new  order  of  things  is  slowly  growing 
up,  and  where,  perhaps,  a  mighty  orb,  whose  dimen- 
sions almost  affright  the  imagination,  is  preparing  for 
its  birth.  And  this  process  is,  after  all,  only  the  pro- 
longation of  the  condensing  of  a  simple  nebula.  Al- 
ready, some  few  of  its  particles  have  come  together  and 
formed  its  secondary  stage ;  and  now  that  secondary 
stage,  which  we  term  a  firmament,  is  passing  into  a 
third,  where  all  the  dispersed  atoms  will  be  gathered 
together,  and  lodged  at  the  centre  of  the  mass  ! 

Our  own  firmament  presents  appearances  which  not 
only  sustain  the  foregoing  conclusions,  through  a  strong 


68  ASTRONOMY. 

analogy,  but  point  the  way  to  still  bolder  thoughts. 
The  Milky  Way  has  been  already  described  as  a  ring, 
for  the  most  part  isolated,  in  which  the  stars  are  very 
dense,  and  where  the  aggregating  power  has  drawn 
them  from  the  general  mass,  and,  by  some  curious  op- 
eration, compressed  them  into  a  crowded  girdle.  But 
neither  is  this  girdle  uniform.  It  is  divided  into  groups, 
chiefly  inclining  to  the  spherical  form,  and  separated 
from  each  other  by  dark  spaces,  like  wrinkles  of  age. 
Sir  William  Herschel  counted  no  less  than  225  such 
groups,  or  subordinate  clusters,  within  the  portion  of  it 
which  he  examined ;  and  as  all  these  were  of  a  kind  to 
mark  the  action  of  gravity,  he  inferred  the  existence 
of  a  clustering  power,  drawing  the  stars  of  it  into  sepa- 
rate groups,  —  a  power  which  had  broken  up  the  uni- 
formity of  the  zone,  and  to  the  irresistible  force  of 
which  it  was  still  exposed.  "  Hence,"  says  he,  in  one 
of  those  bold  moments  in  which  he  fearlessly  traversed 
the  infinities  alike  of  past  and  future,  "  may  we  be 
certain  that  the  stars  will  be  gradually  compressed 
through  successive  stages  of  accumulation  till  they 
come  up  to  what  may  be  called  the  ripening  period 
of  the  globular  cluster,  and  total  insulation  ;  from  which 
it  is  evident  that  the  Milky  Way  must  forcibly  be 
broken  up,  and  cease  to  be  a  stratum  of  scattered  stars. 
We  may  also  draw  an  important  additional  conclusion 
from  the  gradual  dissolution  of  the  Milky  Way  ;  for  the 
state  into  which  the  incessant  action  of  the  clustering 
power  has  brought  it,  is  a  kind  of  chi'onometer,  that 
may  be  used  to  measure  the  time  of  its  past  and  present 
existence.  And  although  we  do  not  know  the  rate  arid 
going  of  this  mysterious  chronometer,  it  is,  nevertheless, 


ASTRONOMY.  69 

certain,  that,  since  a  breaking  up  of  the  parts  of  the 
Milky  Way  affords  a  proof  that  it  cannot  last  forever, 
it  equally  bears  witness  that  its  past  duration  cannot  be 
admitted  to  be  infinite."  Here  is  a  vision  of  unfathom- 
able changes  —  of  the  solemn  march  of  the  majestic 
heavens  from  phase  to  phase,  obediently  fulfilling  their 
awful  destiny. 

If  the  aggregation  of  the  stars  in  the  Milky  Way  still 
goes  on,  as  it  prognosticates,  for  ages,  the  clusters  which 
now,  with  some  intermission,  form  its  ring,  will  become 
isolated,  and  appear  in  the  character  of  separate  sys- 
tems. But'if  this  may  happen  in  future  time,  may  not 
something  similar  have  happened  in  time  past  ?  The 
aspect  of  the  heavens  affords  much  to  countenance  this 
supposition.  We  can  point  out,  for  instance,  a  cluster 
of  a  remarkably  irregular  form,  very  narrow  in  one 
direction,  and  surprisingly  ragged  in  the  edges.  Can 
it  be  possible  that  masses  of  stars  have  been  torn  away 
from  it  in  certain  directions,  so  that  its  thinness  may 
simply  indicate  that,  through  the  action  of  some  irresist- 
ible cause,  parts  of  it  had  there  ripened  sooner  ?  Sin- 
gular to  relate,  it  is  precisely  towards  these  thin  sides, 
and  almost  immediately  beyond  them,  that  the  vast 
mass  of  neighboring  isolated  clusters  is  found  —  clus- 
ters all  spherical,  and  grouping  together  in  extraordi- 
nary proximity. 

But  these  operations  are,  perhaps,  only  types  of  what 
may  have  occurred  on  a  far  more  majestic  scale.  The 
separate  firmaments  which  our  telescopes  have  dis- 
covered show,  even  more  emphatically  than  the  groups 
in  the  Milky  Way,  the  efficacy  and  progress  of  a  clus- 
tering power.  May  not  they  all  have  come  originally 


70  ASTRONOMY. 

from  one  homogeneous  stratum,  or  mass  of  stars,  — so 
that  their  present  isolation,  their  separation,  and  vari- 
ous grouping,  are  only  the  measured  movements  of  the 
clock,  the  gigantic  steps  of  the  hand,  by  which  Time 
records  the  days  of  the  years  of  the  existing  mechanism 
of  the  universe  ?  Stupendous  the  conception,  that  these 
great  heavens  —  the  heavens  which  we  have  deemed 
a  synonyme  of  the  Infinite  and  Eternal  —  are  nothing 
else,  after  all,  than  one  aspect  in  which  matter  is  des- 
tined to  present  itself,  and  that  their  history  is  like  the 
birth,  life,  death,  and  dissolution,  of  the  fragile  plant  ! 
If  this,  indeed,  be  true, — and  the  idea  can  be  supported 
by  many  probabilities,  —  how  immense  the  sphere  of 
real  existence  !  How  little  can  we  ever  know  of  it ! 
at  least,  how  much  must  be  referred  to  that  higher  state 
of  existence,  an  expected  eternity  of  sublime  contem- 
plation ! 


NOTE.  —  In  the  preceding  pages,  under  the  heads  of  "  Nebular 
Stars,"  and  "  Firmamental  Systems,"  we  .have  given  the  state  of 
astronomical  science,  as  generally  received,  at  the  present  time. 
But  some  late  observations,  made  by  a  gigantic  telescope,  executed 
for  Lord  Rosse,  seem  to  render  it  probable  that  the  diffused,  un- 
formed nebulae,  noticed  by  Herschel  and  others,  are  in  fact  only 
groups  of  stars,  too  remote  to  be  separately  distinguished  by  the 
telescopes  they  used.  It  must  now  be  considered  questionable, 
whether  there  are  in  space  any  masses  of  matter  differing  from  the 
solid  bodies  which  compose  planetary  systems. 


PROPERTIES  OF  MATTER. 


MATTER  is  the  general  name  which  has  been  given 
to  every  species  of  substance,  or  thing,  which  is  capable 
of  occupying  space,  or  which  has  the  qualities  of 
length,  breadth,  and  thickness ;  consequently,  every 
thing  which  can  be  seen  or  felt,  is  said  to  be  matter. 
In  describing  the  properties  of  matter,  it  must  be  under- 
stood that  they  do  not  apply  to  the  masses,  or  substances, 
commonly  met  with,  but  to  the  uncompounded  or  prim- 
itive materials  of  which  such  substances  are  formed. 
These  original  component  parts,  of  which  all  substances 


72  PROPERTIES    OF    MATTER. 

are  made  up,  are  styled  simple  matter,  elementary 
principles,  or,  simply,  elements.  The  ancients,  as  is 
well  known,  supposed  that  there  were  but  four  ele- 
ments, or  simple  substances  —  Fire,  Air,  Earth,  and 
Water ;  and  out  of  these,  or  certain  combinations  of 
them,  all  the  substances  in  nature  were  formed.  But 
modern  chemistry,  as  we  shall  show  hereafter,  has  dis- 
covered that  these  elements  are  by  no  means  simple, 
but  capable  of  being  decomposed. 

Every  solid  body,  or  dense  mass,  possesses  what  is 
called  a  centre  of  gravity,  which  is  the  point  upon  or 
about  which  the  body  balances  itself,  and  remains  in  a 
state  of  rest,  or  equilibrium,  in  any  position.  The 
centre  of  gravity  may  be  described  as  a  point  in  solids 
which  always  seeks  its  lowest  level.  In  round,  square, 
and  all  regularly-shaped  bodies,  of  uniform  density  in 
all  their  parts,  the  centre  of  gravity  is  the  centre  of 
these  bodies.  When  a  body  is  shaped  irregularly,  the 
centre  of  gravity  is  the  point  upon  which  the  body  will 
balance  itself,  and  remain  in  a  state  of  rest. 

The  line  of  direction  is  an  ideal  line  drawn  from  the 
centre  of  gravity  of  any  body,  and  passing  to  the 
ground  in  a  direction  perpendicular  to  the  earth's  sur- 
face. When  this  line  falls  within  the  base  of  the  body, 
or  the  part  upon  which  it  stands,  the  body  will  keep  its 
position  ;  but  if  the  line  falls  without  the  base,  the  body 
will  fall,  or  overturn.  By  keeping  this  principle  in 
view,  stability  and  safety  will  generally  be  secured  in 
the  erection  of  works  of  art,  —  such  as  houses,  monu- 
mental edifices,  spires,  steeples, —  as  well  as  in  the  lading 
of  wagons,  and  carts,  and  other  vehicles.  In  every 
instance,  the  base  ought  to  be  sufficiently  large  to 


PROPERTIES    OF    MATTER.  73 

admit  of  the  line  of  direction  falling  within  it.  Through 
ignorance  of  this  principle,  and  from  want  of  expe- 
rience, we  often  see  stage-coaches  and  wagons  laden 
in  such  a  manner  that  their  centre  of  gravity  is  liable 
to  too  great  a  change  of  position,  and  that  they  are 
overturned,  to  the  personal  injury,  and  even  loss  of  life, 
of  the  passengers.  In  the  annexed  cut,  a  loaded  vehicle 


is  represented  as  crossing  the  side  of  a  hill,  which  has 
raised  one  wheel  above  the  level  of  the  other  wheel, 
so  as  to  incline  the  body  of  the  vehicle  very  consider- 
ably from  the  horizontal.  The  centre  of  gravity  is 
represented  in  two  different  positions  ;  a  lower  one  with 
the  line  of  direction  L  C,  and  a  higher  one  with  the 
line  of  direction  U  C.  If  there  had  been  no  load  upon 
the  vehicle,  the  line  of  direction  would  have  remained 
at  L  C ;  and  as  it  falls  within  the  wheel,  or  base,  the 
vehicle  would  have  maintained  its  balance.  But  if  the 
wagon  had  been  laden,  the  centre  of  gravity  would 
have  been  raised,  and,  the  line  of  direction  U  C  conse- 
quently falling  without  the  wheel,  the  vehicle  must 
overturn. 

An  exception  to  this  rule  occurs  in  the  case  of 
xiii. — 7 


74  PROPERTIES    OF    MATTER. 

skaters,  in  making  their  circular  turns  on  the  ice,  in 
which  they  bend,  or  lean,  greatly  beyond  the  perpen- 
dicular position,  without  falling.  This  is  owing  to  the 
contrary  effects  of  centrifugal  force,  a  notice  of  which 
will  next  engage  our  attention.  All  bodies,  in  flying 
round  a  centre,  have  a  tendency  to  proceed  in  a 
straight  line  ;  and  this  principle  of  motion  is  termed 
centrifugal  force.  Examples  of  this  tendency  are 
very  familiar  to  our  observation.  When  we  whirl 
rapidly  a  string  with  an  apple  at  one  end  of  it,  and 
suddenly  allow  the  apple  to  fly  off,  it  proceeds  at  first 
in  a  straight  line,  but  gradually  falls  to  the  earth.  We 
see  many  applications  of  this  principle  every  day ; 
great  use  is  made  of  it,  also,  in  manufactures  and  ma- 
chinery. In  the  grinding  of  corn,  and  in  the  making 
of  pottery  and  glass,  it  saves  much  trouble  and  expense. 
If  a  skater  or  equestrian  should  stand  perfectly  upright 
while  turning  corners  and  describing  circles,  he  would 
inevitably  fall  on  his  side,  being  overturned  by  the  cen- 
trifugal force.  But  by  leaning  inwards,  the  centrifugal 
force  is  counteracted  by  gravity,  and  this  forms  a  sup- 
port to  his  overhanging  body. 

Thus,  centrifugal  force  is  the  tendency  to  fly  off  in  a 
straight  line  from  motion  round  a  centre ;  and  the 
power  which  prevents  bodies  from  thus  flying  off,  is 
called  the  centripetal,  or  centre-seeking  force.  In  the 
case  of  the  apple,  the  centrifugal  force  is  the  impetus 
given  to  the  apple,  which  would  make  it  fly  away,  if 
the  string  were  to  break.  The  centripetal  force  is  the 
string,  which  prevents  it  from  flying  away,  and  gives  a 
circular  direction  to  its  motion. 

It  is  upon  the  mutual  action  of  these  two  forces  that 


PROPERTIES    OF    MATTER.  75 

the  stability  of  the  solar  system  depends.  If  the  ten- 
dency of  the  earth  and  planets  to  gravitate  towards  the 
sun  were  removed,  they  would  fly  off  from  it  in  perfectly 
straight  lines,  and  never  return  ;  and  if  it  were  not  for 
the  centrifugal  force,  which  is  a  result  of  their  circular 
motion,  they  would  rush  to  the  very  body  of  the  sun ; 
and,  in  either  case,  the  harmony  of  the  solar  system 
would  be  entirely  overturned. 

Bodies,  on  being  projected  by  any  impulsive  force, 
are  called  projectiles,  and  are  observed  to  pursue  a 
curvilinear 'and  bent  line  of  direction  in  their  motion. 
The  bending  from  the  straight  line  is  produced  by  the 
force  of  gravity,  and  "  the  ctiange  is  proportional  to  the 
impressed  force ."  A  ball  fired  from  a  cannon,  a  stone 
thrown  from  the  hand,  and  water  spouted  from  a  con- 
fined vessel,  furnish  familiar  examples  of  curvilinear 
motion. 

The  investigation  of  the  paths  which  bodies  describe 
when  thrown,  and  of  many  things  relating  to  their 
motion,  results  in  certain  definite  rules,  called  the  laws 
of  projectiles.  Skilful  generals,  in  bombarding  towns, 
and  attacking  vessels,  at  safe  distances,  take  great  ad- 
vantage of  their  knowledge  of  these  laws. 

There  are  many  very  interesting  circumstances  ecu- 
nected  with  this  subject,  which  our  space  will  not 
allow  us  to  notice. 

Notwithstanding  the  various  substances  which  nature 
offers  to  our  observation  may  differ  essentially  in  touch, 
weight,  and  appearance,  yet  the  elements  of  which 
they  are  composed  all  possess  the  common,  mechanical 
properties  of  matter,  which  properties  are  five  in  num- 
ber— namely,  1.  The  particles  of  matter  are  solid,  and 


76  PROPERTIES    OF    MATTER. 

occupy  space.  2.  They  are  infinitely  divisible. 
3.  They  are  impenetrable.  4.  They  possess  mobil- 
ity, but  are  inert.  5.  They  universally  attract  and 
are  attracted.  The  first  of  these  properties  needs  no 
proof;  for  the  definition  already  given  of  matter  is,  that 
it  has  length,  breadth,  and  thickness ;  and  nothing  can 
have  these  properties  without  occupying  space,  and 
being  solid.  These  characteristics  exist  in  all  matter, 
although  at  first  they  may  be  invisible  :  thus  air,  which 
cannot  be  seen,  is  matter ;  for  if  a  glass  tube,  open  at 
both  ends,  have  its  upper  end  closed  by  the  finger  while 
its  lower  one  is  immersed  in  a  jar  of  water,  it  will  be 
seen  that  the  air  is  material,  and  occupies  its  own 
space  in  the  tube,  for  it  will  not  permit  the  water  to 
enter  it  till  the  finger  is  removed,  when  the  air  will 
escape,  and  the  water  will  rise  to  the  same  level  inside, 
as  outside,  of  the  tube. 

The  second -property  of  matter  is,  that  it  is  infinitely 
divisible  ;  or,  in  other  words,  that  the  original  compo- 
nent parts,  or  elementary  particles,  of  which  all  things 
are  formed,  are  small  beyond  conception.  Thus,  if 
marble,  or  any  other  brittle  substance,  be  reduced  to  the 
finest  powder  which  human  art  can  produce,  its  original 
particles  will  not  be  bruised  or  affected  —  since,  i£  this 
powder  be  examined  by  a  microscope,  each  grain  will 
bs  found  to  be  a  solid  stone,  similar  in  appearance  to 
the  block  from  which  it  was  broken,  and  of  course,  if 
we  possessed  suitable  implements,  would  admit  of  being 
again  subdivided,  or  reduced  to  a  still  finer  powder. 
If  a  single  grain  of  copper  be  dissolved  in  about  fifty 
drops  of  nitric  acid,  and  the  solution  be  afterwards 
diluted  with  about  an  ounce  of  water,  it  is  evident  that 


PROPERTIES   OF    MATTES.  77 

a  single  drop  of  it  must  contain  an  almost  immeasu- 
rably small  portion  of  copper.  Yet,  so  soon  as  this 
comes  in  contact  with  a  piece  of  polished  iron,  or  steel, 
that  metal  will  become  covered  with  a  perfect  coat  of 
copper,  which  shows  how  infinitely  the  copper  can  be 
divided  without  any  alteration  in  its  texture.  Gold  be- 
comes so  attenuated  under  the  hammer,  in  forming  it 
into  gold  leaf,  that  the  500,000th  part  of  a  grain  is 
visible  to  the  naked  eye,  or  the  5,000,000th  part 
through  a  microscope  magnifying  but  ten  times.  It 
has  been  calculated  that  a  pound  of  gold  would  gild  a 
silver  wire  24,000  miles  in  length,  or  capable  of  en- 
compassing the  globe.  But  the  wonders  of  art  sink 
into  nothing  when  compared  to  those  of  nature.  Lee- 
wenhoek,  the  celebrated  microscopic  observer,  affirms, 
that  he  has  counted  two  millions  of  animalculae  in  a 
portion  of  the  roe  of  a  codfish  no  larger  than  a  com 
mon  grain  of  sand. 

That  matter  is  infinitely  divisible,  admits  also  of 
demonstration  on  mathematical  principles ;  for  if  a  par- 
ticle of  matter,  however  small,  be  laid  on  a  plane  sui 
face,  it  must  necessarily  have  an  upper  and  an  under 
part,  or  a  part  which  touches,  and  a  part  which  does 
not  touch,  the  plane. 

The  third  property  of  matter  —  its  impenetrability  — 
seems  to  have  been  adopted  by  Nature,  that  her  works 
might  be  everlasting,  and  incapable  of  wearing  out ;  for, 
although  matter,  in  many  instances,  seems  to  disappear, 
as  in  the  cases  of  burning  and  evaporation,  yet  chem- 
istry distinctly  proves  that  it  is  incapable  of  annihila- 
tion, and  that  the  original  particles,  in  all  cases,  still 
7* 


78  PROPERTIES    OF    MATTER. 

exist,  though,  by  a  change  of  arrangement,  they  are 
made  to  assume  a  different  appearance. 

Mr.  Olmstead,  speaking  of  this  subject,  says,  "  In  all 
the  changes  which  we  see  going  on  in  bodies  around 
us,  not  a  particle  of  matter  is  lost ;  it  merely  changes 
its  form  ;  nor  is  there  any  reason  to  believe  that  there 
is  now  a  particle  of  matter  either  more  or  less  than 
there  was  at  the  creation  of  the  world.  When  we  boil 
water,  and  it  passes  to  the  invisible  state  of  steam,  this, 
on  cooling,  returns  again  to  the  state  of  water,  without 
the  least  loss.  When  we  burn  wood,  the  solid  matter  of 
which  it  is  composed  passes  into  different  forms  —  some 
into  smoke,  some  into  different  kinds  of  airs  or  gases, 
some  into  steam,  and  some  remains  behind  in  the  state 
of  ashes.  If  we  should  collect  all  these  various  prod- 
ucts, and  weigh  them,  we  should  find  the  amount  of 
their  several  weights  the  same  as  that  of  the  body  from 
which  they  were  produced  ;  so  that  no  portion  is  lost 
Each  of  the  substances  into  which  the  wood  was  re- 
solved, is  employed,  in  the  economy  of  nature,  to  con- 
struct other  bodies,  and  may  finally  reappear  in  its 
original  form.  In  the  same  manner,  the  bodies  of 
animals,  when  they  die,  decay,  and  seem  to  perish ;  but 
the  matter  of  which  they  are  composed  merely  passes 
into  new  forms  of  existence,  and  reappears  in  the 
structure  of  vegetables,  or  of  other  animals." 

Even  substances  which  appear  soft,  such  as  air  and 
water,  appear  hard  when  submitted  to  proper  examina- 
tion. Thus  a  quantity  of  water,  falling  in  an  open  tube, 
seems  to  exert  no  particular  force,  on  account  of  the 
resistance  which  it  meets  with  from  the  air ;  but  if  the 


PROPERTIES    OF   MATTER.  79 

air  be  previously  removed  by  the  air-pump,  there  will 
be  no  resistance,  and  the  water  will  sound  like  the  fall- 
ing of  shot,  or  stones.  This  is  called  a  water-hammer. 
Air  differs  from  water  in  being  elastic,  but  its  solidity  is 
shown  by  the  difficulty  of  compressing  a  bladder  filled 
with  it 

The  fourth  property  of  matter — namely,  that  it  pos- 
sesses mobility,  but  is  inert — is  the  constant  object  of 
our  observation.  By  mobility  is  meant,  that  it  may 
always  be  moved  if  a  sufficient  force  be  applied  to 
overcome  its  weight,  or  vis  inertia  :  and  by  being  inert, 
we  understand  that  it  is  inactive,  or  indifferent  to  either 
rest  or  motion,  yet  admits  of  either,  but  always  exerts 
a  power  to  remain  in  that  state  in  which  it  is  found. 
For  instance,  when  a  person  is  riding  on  horseback, 
and  the  horse  suddenly  stops  ;  or  is  in  a  carriage,  or 
boat,  which  is  impeded  by  striking  against  an  obstacle ; 
the  person  is  thrown  forward,  from  his  insensible  en- 
deavor to  remain  in  the  state  of  motion  in  which  he 
then  was.  That  this  is  the  case  with  inanimate  as 
well  as  animate  nature,  will  appear  by  giving  a  sudden 
push  to  a  bowl  of  water,  when  the  water  will  flow  over 
on  the  side  on  which  the  impulse  was  given ;  but  if 
once  the  bowl  is  put  in  motion,  and  then  suddenly 
stopped,  it  will  flow  over  on  the  opposite  side.  Num- 
berless other  instances  may  be  found,  in  the  difficulty 
of  putting  heavy  bodies,  such  as  ships,  loaded  wagons, 
&c.,  into  motion.  From  this  property  of  matter,  if  a 
stone  or  any  inanimate  mass  is  undisturbed,  it  will  re- 
main forever  motionless ;  and  when  once  put  into  mo- 
tion, would  continue  in  it,  and  move  forever,  were  it  not 
prevented  by  the  resistance  of  the  air,  and  by  friction. 


80  PROPERTIES    OF    MATTER. 

Attraction  is  the  fifth  property  of  matter,  and  exists 
in  every  individual  particle.  All  matter  attracts,  and  is 
attracted,  in  proportion  to  its  quantity  ;  therefore,  all 
things  upon  the  earth  incline,  or  are  drawn,  towards  its 
centre,  because  the  earth  is  the  largest  mass  of  matter 
in  their  immediate  vicinity.  There  are  several  kinds 
of  attraction  —  distinguished  by  the  names  of  cohe- 
sion and  gravitation  —  magnetic,  electric,  and  elective 
attraction,  or  affinity.  These,  in  their  general  effects,  — 
with  the  exception  of  the  last,  —  appear  nearly  similar, 
although  they  depend  upon  different  circumstances. 

The  attraction  of  cohesion  is  that  power  which  unites 
the  separate  or  individual  particles  of  matter,  and  forms 
them  into  masses,  or  bodies.  This  attraction,  in  general, 
does  not  extend  to  any  sensible  distance  from  the  body  ; 
and  hence,  when  the  parts  of  any  substance  are  sep- 
arated or  broken,  it  is  difficult  to  unite  them.  But  if 
they  can  be  brought  into  sufficiently  close  contact,  this 
attraction  operates,  and  they  are  joined.  On  this  prin- 
ciple, two  pieces  of  hot  iron  may  be  hammered  together 
and  united.  A  plate  of  lead,  and  one  of  tin,  passed 
together  through  a  flatting-mill,  become  combined 
into  one  plate  of  metal.  Glues,  cements,  and  solders, 
act  in  the  same  manner,  upon  the  respective  substances 
to  which  they  are  applied,  by  stopping  up  the  pores,  or 
interstices,  and  making  the  contact  more  perfect.  The 
agency  of  this  principle  is  shown  by  pressing  two  lead 
planes  together,  when  they  will  adhere  so  firmly  as  to 
require  considerable  force  to  separate  them ;  and  the 
increasing  ratio  of  this  attraction,  as  bodies  approach 
each  other,  is  very  well  shown  by  floating  two  corks  on 
the  surface  of  the  water,  when  they  will  run  together 


PROPERTIES   OF   MATTER.  81 

with  an  accelerated  motion.  The  power  which  holds 
all  things  to  the  earth's  surface  is  this  same  attraction ; 
but  when  spoken  of  as  applying  to  worlds,  it  is  called 
the  attraction  of  gravitation. 

As  the  attraction  of  cohesion  is  common  to  all 
matter,  it  would  appear  that  particles  of  every  descrip- 
tion must  indiscriminately  cohere  and  stick  together, 
and  form  substances ;  and,  consequently,  that  an  infinite 
variety  of  compounds  would  be  found  in  nature,  with 
almost  an  impossibility  of  any  two  of  them  being  alike. 
Such  would,  undoubtedly  be  the  case,  were  it  not 
for  that  modification  of  attraction  called  affinity,  or 
elective  attraction:  this,  however,  belongs  rather  to 
chemistry,  than  to  the  present  division  of  our  subject 
By  this  power,  the  general  effects  of  cohesion  are 
restrained,  and  only  one  particular  species  of  matter 
will  unite  with  another,  unless,  in  some  cases,  by  the 
interposition  of  a  third  or  fourth  material ;  in  conse- 
quence of  which,  only  a  definite  number  of  natural 
substances  are  formed,  and  the  same  thing  always 
appears  with  nearly  similar  characteristics. 

Capillary  attraction  is  that  species  of  attraction  by 
which  fluids  are  raised  in  small  tubes,  and  is  a  modifi- 
cation of  the  attraction  of  cohesion.  If  a  capillary 
tube,  or  tube  of  very  small  diameter,  be  immersed  in 
fluid,  that  fluid  will  rise  to  a  certain  height  in  it  pro- 
portionate to  the  size  of  its  base,  rising  highest  in  the 
narrowest  tubes.  This  depends  on  the  cohesive  at- 
traction exerted  by  the  sides  of  tHe  tube,  and  accounts 
for  sap  rising  in  the  pores  or  tubes  of  vegetables. 
The  increasing  force  of  this  attraction  with  the  di- 
minished size  of  the  tube,  is  beautifully  shown  by  two 
F 


82  PROPERTIES    OF    MATTER. 

square  glass  planes,  touching  at  one  edge,  and  sep- 
arated at  the  opposite  one  by  a  wedge.  On  immers- 
ing these  in  water,  and  then  raising  them  out  of  it,  a 
portion  of  the  water  will  be  retained  in  that  mathe- 
matical curve  denominated  an  hyperbola.  Capillary 
attraction  also  causes  fluids  to  rise  in  sponges,  sugar, 
sand,  and  other  porous  bodies,  as  soon  as  they  come 
into  contact  with  them. 

The  comparative  density  of  bodies  —  by  which  is 
meant  their  variation  in  weight  while  of  the  same 
dimensions  —  most  probably  depends  upon  their  original 
molecules,  or  atoms,  being  of  such  forms,  and  so  dis- 
posed, as  to  admit  of  their  coming  into  more  or  less 
close  contact.  Thus  a  greater  number  of  particles  will 
pack,  or  lie,  in  any  given  space,  if  their  forms  are 
regular,  than  could  do  so  were  they  irregular.  For 
example,  it  may  be  supposed  that  1,000,000  particles 
of  gold  are  contained  in  a  cubic  inch  of  that  metal : 
500,000  particles  of  iron  might  also  be  capable  of 
occupying  the  same  space,  and  100,000  particles  of 
wood.  In  the  iron  and  wood  there  must,  therefore,  be 
many  more  pores,  or  interstices,  than  in  the  gold ;  and 
of  course  the  gold  will  be  the  heaviest,  or  most  dense. 
This  increased  density  and  weight  do  not  therefore 
arise  from  the  individual  particles  of  gold  being 
heavier  than  those  of  wood,  but  from  a  greater  num- 
ber of  them  being  forced  into  the  same  space ;  for  the 
original  particles  of  matter  are  presumed  to  be  all  of 
the  same  weight;  arM  thus  gold,  which  is  one  of  the 
heaviest  solids,  will,  when  dissolved,  remain  suspended 
in  ether,  which  is  the  lightest  of  all  visible  fluids.  It 
is  impossible  to  obtain  the  absolute  weight  of  bodies 


PROPERTIES   OF    MATTER.  83 

which  vary  in  density,  by  weighing  them  in  the  open 
air,  for  the  air  will  buoy  up  that  which  has  the  least 
density  more  than  that  which  has  the  greatest  And 
thus,  although  a  piece  of  cork  and  a  piece  of  lead  may 
exactly  balance  each  other  at  the  ends  of  a  scale-beam, 
yet  that  balance  will  be  destroyed  as  soon  as  they  are 
placed  in  an  exhausted  receiver ;  for  then  the  cork,  by 
losing  the  buoyant  assistance  of  the  air,  will  preponder- 
ate ;  thereby  proving  that  it  contains  more  matter  than 
the  lead,  though  not  in  the  same  compass.  This  prin- 
ciple is  sometimes  further  elucidated  by  the  experiment 
of  letting  a  guinea  and  a  featner  fall  together  in  a  glass 
receiver:  when  this  is  full  of  air,  the  guinea  falls  while 
the  feather  is  floating  about ;  but  when  the  air  is  with- 
drawn from  the  receiver,  they  both  reach  the  bottom  at 
the  same  instant. 

Since  the  earth  is  of  a  globular  form,  and  the  power 
of  attraction  is  in  proportion  to  the  quantity  of  matter, 
so,  of  course,  the  inhabitants,  and  all  things  upon  the 
earth's  surface,  will  be  attracted,  or  drawn  downwards, 
in  a  direction  tending  to  its  centre;  for  since  the 
longest  line  which  can  be  drawn  through  a  circle,  or 
globe,  is  a  diameter  which  must  pass  through  its 
centre,  so  this  will  likewise  pass  through  the  greatest 
quantity  of  matter  contained  in  any  one  directica  in  it, 
and  consequently  all  bodies  will  fall  in  a  direction 
pointing  to  the  centre  of  the  earth.  Hence  the  use 
of  plumb-lines  for  obtaining  perpendiculars  to  the 
horizon,  for  setting  the  sides  of  buildings  upright,  &c. 

Besides  the  above-described  five  properties  of  mat- 
ter, it  possesses  yet  another  property,  of  great  impor- 
tance —  namely,  its  power  of  arrangement,  commonly 


84  PROPERTIES    OF   MATTER. 

called  polarity.  The  attraction  of  cohesion  sufficiently 
accounts  for  the  formation  of  masses,  or  substances,  by 
drawing  the  original  particles  of  matter  together,  and 
then  holding  them  in  contact ;  but  it  is  found  that  they 
are  not  only  drawn  and  held  together,  but  that  the  same 
matter  always  takes  the  same  arrangement,  or  forma- 
tion. Thus  a  piece  of  iron,  tin,  or  any  other  metal,  or 
mineral,  will,  when  broken,  always  exhibit  the  same 
arrangement  and  disposition  of  parts,  or  grain,  as  it  is 
generally  called.  And  so  strictly  are  the  laws  of 
combination  found  to  prevail  in  the  union  of  elements, 
and  formation  of  substances,  that  a  novel  and  important 
character  is  given  to  modern  chemical  researches,  ap- 
proaching almost  to  mathematical  precision ;  it  being 
ascertained  not  only  that  the  same  materials  will,  in 
most  cases,  assume  the  same  form,  but  that  the  ingre- 
dients which  enter  into  the  composition  of  substances 
do  so  in  certain  definite  proportions,  which  cannot  be 
changed  without  also  changing  the  character  of  the 
substance  they  form. 


THE   MECHANICAL   POWERS, 


THE  Mechanical  Powers  are  certain  simple  arrange- 
ments of  machinery,  by  means  of  which  weights  may 
be  raised,  or  resistance  overcome,  with  the  exertion  of 
less  power,  or  strength,  than  is  necessary  without  them. 
In  a  mechanic  power,  the  weight,  or  resistance,  to  be 
acted  upon,  and  the  power,  or  strength,  which  acts  upon 
it,  should  both  move  at  the  same  time  ;  and  any  thing 
constitutes  a  mechanic  power,  in  which  the  motion  of 
the  power  produces  a  simultaneous  motion  in  the 
resistance,  provided  less  power  is  necessary  than  is 
due  to  the  weight,  or  strength,  of  such  resistance. 
From  this  general  definition,  it  might  appear  that 
xiii. — 8 


86  THE    MECHANICAL    POWERS. 

every  machine  capable  of  generating  force  would  be 
a  mechanic  power ;  but  simplicity  is  likewise  essential, 
and  hence  the  mechanical  powers  may  be  said  to  be 
the  elements  of  machinery ;  and  they  are,  in  fact,  so 
elementary  as  to  admit  of  no  simplification  or  altera- 
tion. They  are  but  six  in  number ;  and  the  names  by 
which  they  are  distinguished  are,  the  LEVER,  the 

WHEEL   AND   AXLE,   the    PULLEY,   the    INCLINED     PLANE, 

the  WEDGE,  and  the  SCREW.  Out  of  the  whole,  or  a 
part,  of  these,  it  will  be  found  that  every  mechanical 
engine,  or  piece  of  machinery,  is  constructed. 

THE  LEVER.  This  is  the  simplest  of  all  the  me- 
chanical powers,  and  is  generally  considered  the  first. 
It  is  an  inflexible  bar,  or  rod,  of  any  kind  or  shape,  so 
disposed  as  to  turn  on  a  pivot,  or  prop,  which  is  always 
called  \\sfulcrum.  It  has  the  weight,  or  resistance,  to 
be  overcome,  attached  to  some  one  part  of  its  length, 
and  the  power  which  is  to  overcome  that  resistance 
applied  to  another;  and  as  the  power,  resistance,  and 
fulcrum  admit  of  various  positions  with  regard  to  each 
other,  so  the  lever  is  divided  into  three  modifications, 
distinguished  as  the  first,  second,  and  third  kinds  of 
lever  —  that  portion  of  it  which  is  contained  between 
the  fulcrum  and  the  power  being  called  the  acting  part, 
or  arm,  of  the  lever ;  and  that  part  which  is  between 
the  fulcrum  and  the  resistance,  its  resisting  part,  or 
arm. 

A  beam,  or  rod,  of  any  kind,  resting  at  one  part  on  a 
prop,  or  axis,  which  becomes  its  centre  of  motion,  is  a 
lever;  and  it  has  been  so  called,  probably,  because 
such  a  contrivance  was  first  employed  for  lifting 
weights.  This  figure  represents  a  lever  used  to  move 


THE    MECHANICAL    POWERS.  87 


a  block  of  stone  :  a  is  the  end  to  which  the  power,  or 
force,  is  applied ;  b  is  the  prop,  or  fulcrum  ;  and  c  is  the 
weight,  or  resistance :  this  is  a  simple  crowbar,  or  hand- 
spike. According  to  a  fundamental  principle  of  dy- 
namics, the  power  may  be  as  much  less  intense  than 
the  resistance  as  it  is  farther  from  the  fulcrum,  or 
moving  through  a  greater  space.  A  man  at  a,  there- 
fore,—  twice  as  far  from  the  prop  as  the  centre  of  grav- 
ity of  the  weight,  i,  —  will  be  able  to  lift  a  weight  twice 
as  heavy  as  himself ;  but  he  will  lift  it  only  one  inch 
for  every  two  that  he  descends  ;  for  it  is  also  a  principle 
of  this  science  that  what  is  gained  in  power  is  lost  in 
time. 

There  is  no  limit  to  the  difference  of  intensity  in 
forces  which  may  be  placed  in  opposition  to  each  other 
by  the  lever,  except  the  length  and  strength  of  the 
material  of  which  the  levers  must  be  formed.  Every 
one  has  heard  of  the  boast  of  Archimedes,  "  Give  me 
a  lever  long  enough,  and  a  prop  strong  enough,  and 
with  my  own  weight  I  will  move  the  world  !  "  But  he 
must  have  moved  with  the  velocity  of  a  cannon-ball 
for  millions  of  years,  to  alter  the  position  of  the  earth 


08  THE    MECHANICAL    POWERS. 

half  an  inch.  In  mathematical  truth,  this  feat  of 
Archimedes  is  performed  by  every  man  who  leaps 
from  the  ground,  for  he  kicks  the  world  away  from 
him  when  he  rises,  and  attracts  it  again  when  he  falls 
back. 

The  common  claw-hammer  for  drawing  nails  is  a 
striking  example  of  the  power  of  a  lever  of  this  de- 
scription. A  boy  who  cannot  exert  a  direct  force  of 
fifty  pounds  may,  by  means  of  this  kind  of  hammer, 
extract  a  nail  to  which  half  a  ton  may  be  suspended, 
because  his  hand  moves  eight  inches,  perhaps,  to  make 
the  nail  rise  one  quarter  of  an  inch.  The  claw-ham- 
mer also  proves  that  it  is  of  no  consequence  whether 
the  lever  be  straight  or  crooked,  provided  it  produces 
the  required  difference  of  velocity  between  power 
and  resistance.  The  part  of  the  hammer  resting  on 
the  plank  is  the  fulcrum.  Pincers,  or  forceps,  are 
double  levers,  and  so  are  common  scissors.  The  steel- 
yard is  a  lever  with  unequal  arms. 

The  second  kind  of  lever  possesses  the  same  degree 
of  power  with  the  first,  and  operates  with  the  same 
results.  The  third  kind  cannot  be  called  a  mechanical 
power,  for,  since  its  resting  arm  is  longer  than  the 
acting  arm,  it  must  lose  power,  though  it  gains  time. 
The  most  familiar  examples  of  the  occurrence  of  this 
kind  of  lever,  are  in  the  use  of  common  fire-tongs, 
and  in  rearing  a  tall  ladder  against  a  wall.  But  the 
circumstance  that  principally  gives  importance  to  it,  is, 
that  the  limbs  of  men  and  all  animals  are  formed  of  it ; 
for  the  bones  are  levers,  the  joints  are  the  fulcra, 
while  the  muscles  which  give  motion  to  the  limbs,  or 


THE    MECHANICAL   POWERS.  89 

produce  the  power,  are  inserted  and  act  close  to  the 
joints,  causing  action  at  the  extremities. 

To  calculate  the  effect  of  a  lever  in  practice,  we 
must  always  take  into  account  the  weight  of  the  lever 
itself,  and  its  bending.  But  in  speaking  of  the  theory 
of  the  lever,  we  usually  leave  these  out  of  the  question 
considering  it  as  a  rod  without  weight  or  flexibility. 

THE  WHEEL  AND  AXLE.  This  power  consists  of 
two  parallel  wheels,  pulleys,  cylinders,  or  circles,  having 
one  axis  in  common.  The  letter  d  here  marks  the 


wheel,  and  c  an  axle  affixed  to  it.  We  see  that,  in  turn 
ing  together,  the  wheel  would  take  up,  or  throw  off,  as 
much  more  rope  than  the  axle  as  the  circumference 
of  the  wheel  is  greater  than  that  of  the  axle.  If  the 
proportions  were  as  four  to  one,  one  pound,  at  i,  hang- 
ing from  the  circumference  of  the  wheel,  would  balance 
four  pounds  at  a,  hanging  from  the  opposite  side  of 
the  axle.  A  common  crane  for  raising  weights  con- 
sists of  an  axle,  to  wind  up,  or  receive,  the  rope  which 
carries  the  weight,  and  of  a  large  wheel,  at  the  circum- 
ference of  which  the  power  is  applied.  The  power 
may  be  animal  effort  on  the  outside  of  the  wheel,  or 
8* 


90  THE    MECHANICAL    POWEES. 

the  weight  of  a  man,  or  beast,  walking  on  the  inside, 
and  moving  it  as  a  squirrel  moves  the  cylinder  of  his 
cage. 

By  means  of  a  wheel  which  is  very  large  in  propor- 
tion to  its  axle,  force  of  very  different  intensities  may 
be  balanced,  but  the  machine  becomes  of  inconvenient 
proportions.  It  is  found  preferable,  therefore,  when  a 
great  difference  of  velocity  is  required,  to  use  a  com- 
bination of  wheels,  of  moderate  size.  In  the  following 
figure,  three  wheels  are  seen  thus  connected.  Teeth 


in  the  axle,  d,  of  the  first  wheel,  c,  acting  on  six  times 
the  number  of  teeth  in  the  circumference  of  the  second 
wheel,  g,  turn  it  only  once  for  every  six  times  that  c 
revolves.  In  the  same  manner  the  second  wheel,  by 
turning  six  times,  turns  the  third  wheel,  h,  once  ;  the  first 
wheel  therefore  turns  thirty-six  times  for  one  tarn  of 
the  last ;  and  as  the  diameter  of  the  wheel  c,  to  which 
the  power  is  applied,  is  three  times  greater  than  that 
of  the  axle,  which  has  the  resistance,  three  times  36, 
or  108,  is  the  difference  of  velocity :  — therefore  1 
pound  at  b  will  balance  108  pounds  at  a. 


THE   MECHANICAL   POWERS.  91 

On  the  principle  of  combined  wheels,  cranes  are 
made,  by  which  one  man  can  lift  many  tons.  It  is 
even  possible  to  make  an  engine,  by  means  of  which  a 
little  windmill,  of  a  few  inches  hi  diameter,  could  'ear 
up  the  strongest  oak  by  the  roots ;  but  of  course  this 
would  require  a  long  rime  for  its  work.  The  most 
familiar  instances  of  wheel-work  are  in  our  clocks  and 
watches.  One  turn  of  the  axle  on  which  the  watch- 
key  is  fixed,  is  rendered  equivalent,  by  the  train  of 
wheels,  to  about  400  turns,  or  beats,  of  the  balance- 
wheel  ;  and  'thus  the  exertion,  during  a  few  seconds,  of 
the  hand  which  winds  it  up,  gives  motion  for  24  or  30 
hours.  By  increasing  the  number  of  wheels,  time- 
pieces are  made  which  go  for  a  year;  and  if  the  ma- 
terial would  last,  they  might  easily  be  made  to  go  for 
a  thousand  years. 


THE  IXCLHS-ED  PLAXE  is  described  by  the  above  cut. 
A  force  pushing  a  weight  from  C  to  D,  only  raises  it 
through  the  perpendicular  height,  E  D,  by  acting  along 
the  whole  length  of  the  plane,  C  D ;  and  if  the  plane 
be  twice  as  long  as  it  is  high,  one  pound  at  B,  acting 
over  the  pulley,  D,  would  balance  two  pounds  at  A,  or 
any  where  on  the  plane ;  and  so  of  all  other  quantities 
and  proportions.  A  horse  drawing  on  a  road  where 
there  is  a  rise  of  one  foot  in  twenty,  is  really  lifting 
one  twentieth  of  his  load,  as  well  as  overcoming  the 
friction  and  other  resistance  of  the  carriage.  Hence 


92  THE    MECHANICAL   POWERS. 

the  importance  of  making  roads  as  level  as  possible  ; 
and  hence  the  error,  which  has  often  been  committed, 
of  carrying  roads  directly  over  hills,  for  the  sake  of 
straightness,  when,  by  going  round  the  bases  of  the 
hills,  the  distance  would  scarcely  have  been  increased, 
and  all  rising  and  falling  would  have  been  avoided. 
Hence,  also,  a  road  up  a  very  steep  hill  must  be  made 
to  wind,  or  go  zigzag,  all  the  way ;  for,  to  reach  a 
given  height,  the  ease  of  the  pull  to  the  horses  is 
greater,  exactly  as  the  road  is  made  longer.  An  in- 
telligent driver,  in  ascending  a  steep  hill  by  a  broad 
road,  winds  from  side  to  side  all  the  way,  to  save  his 
horses  what  little  he  can. 

Hogsheads  of  merchandise,  which  twenty  men  could 
not  lift  by  applying  their  strength  directly,  are  often 
seen  moved  out  of,  or  into,  wagons  by  one  or  two  men 
who  have  the  assistance  of  inclined  planes.  On  some 
canals  and  railroads,  the  loaded  boats  and  cars  are 
drawn  up  by  machinery  on  inclined  planes.  It  is  sup- 
posed that  the  ancient  Egyptians  must  have  used  this 
mechanical  power  to  assist  in  elevating  and  placing 
those  immense  masses  of  stone  with  which  their  pyra- 
mids and  other  gigantic  piles  of  architecture  were 
constructed. 

In  our  speculations  upon  the  power  of  the  inclined 
plane,  we  suppose  the  plane  to  be  perfectly  smooth, 
and  that  bodies  move  upon  it  without  friction  or  imped- 
iment ;  but  this  can  never  be  the  case  in  practice,  even 
in  the  most  perfect  machines;  consequently,  some 
allowance  must  be  made  from  the  calculated  effect, 
and  when  carriages  move  jipon  rough  or  sandy  roads, 
this  allowance  must  be  considerable. 


THE   MECHANICAL  POWERS.  93 

THE  PULLET.    A  pulley  is  a  grooved  wheel,  around 
which  a  rope  is  passed,  and  is  either  fixed  or  movable. 


The  preceding  cut  represents  a  fixed  pulley,  which 
never  changes  its  position :  a  is  the  wheel ;  I  a  beam,  or 
roof,  from  which  the  wheel  is  suspended  ;  c  is  the  power 
hanging  at  one  end  of  the  rope ;  and  d  is  the  weight  at  the 
other  end.  In  such  a  construction,  it  is  evident  that  the 
weight  —  for  instance,  ten  pounds — is  equally  supported 
by  each  end  of  the  rope,  and  that  a  man  holding  up 
one  end,  only  bears  half  of  it,  or  five  pounds ;  but  to 
raise  the  weight  one  foot,  he  must  draw  up  two  feet  of 
rope ;  therefore,  with  the  pulley,  he  lifts  five  pounds 
two  feet,  when  he  would  be  obliged  to  lift  ten  pounds 
one  foot  without  the  pulley. 

This  kind  of  pulley,  however,  possesses  no  mechan- 
ical advantage.  To  raise  a  pound  weight  from  the 
ground  at  one  end  of  the  cord,  the  power  of  one  pound 
must  be  exerted  at  the  other.  Its  object,  then,  is  not  to 
save  power,  but  to  give  convenience  in  pulling.  For 
instance,  by  pulling  downwards,  a  weight  may  be  raised 
upwards ;  or,  by  pulling  in  one  direction,  a  load  may  be 
made  to  proceed  in  another.  Thus,  in  drawing  a 
bucket  out  of  a  well,  it  is  much  easier  to  pull  down- 
wards, by  means  of  a  rope  passing  through  a  pulley 


94 


THE    MECHANICAL   POWERS. 


over  the  head,  than  upwards,  by  drawing  directly  at  the 
bucket. 

Many  wheels  may  be  combined  together,  and  in 
many  ways,  to  form  compound  pulleys.  Wherever 
there  is  but  one  rope 'running  through  the  whole,  as 


snown  here,  the  relation  of  power  and  resistance  is 
known  by  the  number  of  folds,  or  turns,  of  the  rope 
which  supports  the  weight.  Here  are  six  turns,  and  a 
power  of  one  hundred  pounds  would  balance  a  resistance 
of  six  hundred.  The  chief  use  of  this  pulley  is  on  board 
ships,  where  it  is  called  a  Hock.  It  aids  so  powerfully 
in  hoisting  the  masts  and  sails,  &c.,  that,  by  means  of  it, 
a  small  number  of  sailors  are  rendered  equal  to  the 
duties  of  a  large  ship. 

There  is  no  assignable  limit  to  the  power  which  may 
be  exerted  by  means  of  pulleys.  A  machine  may  be 
constructed  to  raise  with  ease  any  weight  which  the 
strength  of  the  materials  will  bear,  provided  the  com 


THE   MECHANICAL   POWERS.  95 

bination  be  not  so  complex  as  to  exhaust  the  power  by 
the  friction  produced. 

THE  WEDGE.  This  power  acts  on  the  principle  of 
an  inclined-plane  force  moving  forward  between  resist- 
ances, to  overcome  or  separate  them,  instead  of  being 
stationary,  while  the  resistance  is  moved  along  its  sur- 
face. The  same  rule,  as  to  mechanical  advantage,  has 


been  applied  to  both  cases,  the  force  acting  on  the 
wedge  being  considered  as  moving  through  a  space 
equal  to  its  length,  C  D,  and  the  resistance  as  yielding 
through  a  space  equal  to  its  breadth,  A  B.  But  this  rule 
is  far  from  explaining  the  extraordinary  power  of  the 
wedge.  It  appears  that,  during  the  tremor  produced 
by  the  blow  of  the  driving-hammer,  the  wedge  insin- 
uates itself,  and  advances  much  more  quickly  than  the 
above  rule  anticipates.  The  wedge  is  used  for  many 
purposes,  as  for  splitting  blocks  of  stone  and  wood ; 
for  squeezing  strongly,  as  in  the  oil-press ;  for  lifting 
great  weights,  as  when  a  ship  of  war,  in  dock,  is  raised 
by  driving  wedges  under  her  keel.  An  engineer  in 
London,  who  had  built  a  very  lofty  and  heavy  chimney 
for  his  steam  engines  and  furnaces,  found,  after  a  time, 


96  THE    MECHANICAL   POWERS. 

that  it  was  beginning  to  lean  on  one  side.  By  driving 
wedges  under  that  side,  he  succeeded  in  restoring  it  to 
a  complete  perpendicular. 

The  wedge  is  the  least  used  of  the  simple  mechan- 
ical powers,  but  the  principle  upon  which  it  acts  is  in 
extensive  application.  Needles,  awls,  bodkins,  and 
driving  nails,  are  the  most  common  examples.  Knives, 
swords,  razors,  the  axe,  chisel,  and  other  cutting  instru- 
ments, also  act  on  the  principle  of  the  wedge  ;  so  like- 
wise does  the  saw,  the  teeth  of  which  are  small 
wedges,  and  act  by  being  drawn  along  while  pressed 
against  the  object  operated  upon.  When  the  edge  of 
a  scythe,  or  razor,  is  examined  with  a  microscope,  it  is 
seen  to  be  a  series  of  small,  sharp  angularities,  of  the 
nature  of  the  teeth  of  a  saw. 

THE  SCREW  may  be  considered  as  a  winding  wedge  ; 
for  it  has  the  same  relation  to  a  straight  wedge  that  a 
road,  winding  up  a  hill  or  town,  has  to  a  straight  road 
of  the  same  length  and  acclivity.  A  screw  may  be 


described  as  a  spindle,  a  d,  with  a  thread  wound  spirally 
round  it,  turning  or  working  in  a  nut,  c,  which  has  a 
corresponding  spiral  furrov^  fitted  to  receive  the  thread. 
Every  turn  of  the  screw  carries  it  forward  in  a  fixed 
nut,  or  draws  a  movable  nut  along  upion  it,  by  exactly 


THE    MECHANICAL   POWERS.  97 

.he  distance  between  two  turns  of  its  thread  ;  this  dis- 
tance, therefore,  is  the  space  described  by  the  resist- 
ance, while  the  force  moves  in  the  circumference  of 
the  circle  described  by  the  handle  of  the  screw,  as  at  i, 
in  the  figure.  The  disparity  between  these  lengths,  or 
spaces,  is  often  as  a  hundred,  or  more,  to  one ;  hence 
the  prodigious  effects  which  a  screw  enables  a  small 
force  to  produce.  Screws  are  much  used  in  presses 
of  all  kinds ;  as  in  those  for  squeezing  oil  and  juice 
from  vegetable  bodies,  as  linseed,  rape-seed,  almonds, 
apples,  grapes,  sugar-cane,  &c.  •  They  are  used  in  the 
cotton-press,  which  reduces  a  great  spongy  bale,  of 
which  a  few,  comparatively,  would  fill  a  ship,  to  a  dense 
package  heavy  enough  to  sink  in  water ;  and  in  the 
common  printing-press,  which  forces  the  paper  strongly 
against  the  types.  The  screw  is  the  great  agent  in  the 
coining  machinery  of  mints. 

As  a  screw  can  easily  be  made  with  a  hundred  turns 
of  its  thread  in  the  space  of  an  inch,  and  at  perfectly 
equal  distances  from  each  other,  it  enables  the  mathe- 
matical instrument  maker  to  mark  divisions  on  his 
work  with  a  minuteness  and  accuracy  quite  extraor- 
dinary. When  a  screw  is  at  liberty  to  move  equally  in 
all  directions,  it  is  simply  called  a  screw  ;  but  when  it  is 
confined  at  its  ends,  so  that  it  can  merely  revolve,  with- 
out advancing  or  withdrawing,  it  is  called  an  endless 
screw, — and  in  this  case  it  generally  acts  into  the  teeth 
of  a  wheel,  either  to  move  or  be  moved  by  mat  wheel ; 
but  its  power  is  alike  in  both  cases.  The  screw,  though 
a  mechanical  power,  can  hardly  be  called  a  simple 
instrument,  because,  from  its  great  friction,  it  always 
requires  the  assistance  of  a  lever  to  turn  it ;  and  when 
G  mx — 0 


98  THE    MECHANICAL   POWERS. 

so  turned,  its  power  is  estimated  by  taking  its  circum- 
ference, and  dividing  this  by  the  distance  between  any 
two  of  its  threads. 

Yet,  after  all,  there  seems  to  be  no  reason,  except 
long-established  usage,  why  the  appellation  of  Me- 
chanical Powers  should  be  restricted  to  the  six  contri- 
vances above  explained  ;  for  many  others  equally  de- 
serve it ;  and,  in  fact,  the  mightiest  of  all  mechanical 
devices,  the  steam  engine,  does  not  derive  its  power 
from  solid  substances  at  all. 


HYDROSTATICS. 


THIS  science  has  for  its  object  the  examination  of 
the  mechanical  laws  which  regulate  the  motions, 
pressure,  gravitation,  and  equilibrium,  of  inelastic  fluids, 
as  well  as  their  effects  upon  bodies  which  floaKupon 
or  are  immersed  in  them.  The  construction  of  pumps 
and  machines  for  raising  and  conveying  water,  and  of 
machinery  to  be  moved  by  it,  is  made  a  separate 
branch  of  the  same  inquiry,  under  the  name  of  HY- 
DRAULICS, which  will  be  the  subject  of  the  next  chapter. 

The  incompressibility  of  water  had  long  been  sus- 
pected, but  was  first  fairly  put  to  the  test  in  the  Acade- 
my del  Cimento  at  Florence,  La  1650.  A  quantity  of 
pure  water  was  introduced  into  a  hollow  sphere  of  gold, 
as  being  the  most  dense  and  compact  metal,  and  a  screw, 
working  in  a  water-tight  joint,  was  then  forced  into  the 
globe  among  the  water,  by  which  it  was  compressed 
with  great  force;  and  it  was  found  that  the  water 
refused  to  admit  of  this  compression,  but  actually 
oozed  through  the  pores  of  the  metal,  and  appeared 
like  dew  on  the  outside  of  the  globe.  This  process  is 
called  the  Florentine  experiment. 

Mr.  Canton  afterwards  repeated  this  experiment  in  a 
very  accurate  manner,  and  with  some  variation  of 
form.  He  enclosed  a  quantity  of  mercury  in  a  glass 


100  HYDROSTATICS. 

tube  similar  to  those  used  for  thermometers,  but  of 
greater  dimensions,  and  he  observed  to  what  point  the 
mercury  rose  when  the  whole  was  heated  to  50  de- 
grees of  Fahrenheit :  after  this,  the  mercury  was  made 
to  expand,  by  increased  heat,  until  the  whole  tube  was 
filled,  and  in  this  state  its  end  was  hermetically  sealed. 
The  mercury,  being  thus  relieved  from  the  pressure  of 
the  atmosphere,  did  not  fall  down  to  its  original  situa- 
tion, but  stood  nearly  a  third  of  an  inch  higher  than 
before,  by  which  mercury  was  proved  to  be  an  ex- 
pansible, and  consequently  a  compressible,  fluid.  The 
tube  was  now  emptied  ;  and  water  which  had  been  long 
boiled,  to  clear  it  from  any  air  which  it  might  contain, 
was  substituted  in  the  place  of  mercury,  and  treated  in 
the  same  manner.  The  water  was  found  to  stand 
nearly  half  an  inch  higher,  when  relieved  from  at- 
mospheric pressure,  than  it  did  before ;  from  which  it 
was  inferred  that  water  is  slightly  compressible,  though 
to  so  small  a  degree  as  to  be  of  no  consequence  in 
practice. 

This  experiment,  however,  was  on  a  very  small  scale, 
and  nothing  further  was  done  towards  ascertaining  the 
degree  of  condensation  that  water  would  admit  of,  till 
Mr.  Perkins,  an  American,  tried  some  very  ingenious 
and  decisive  experiments  upon  it.  He  was  first  led  to 
the  subject  by  the  contemplation  of  a  simple,  but 
hitherto  unexplained  fact ;  namely,  that,  when  a  bottle, 
completely  filled  with  water,  well  corked  and  secured, 
was  sunk  into  the  deep  sea  by  a  heavy  weight,  k  always 
returned  again  to  the  surface,  either  with  the  cork 
pushed  into  the  inside,  or  protruded  in  a  greater  or  less 
degree  ;  but  the  water  in  the  bottle  was,  in  all  cases, 


HYDROSTATICS.  101 

turned  from  fresh  to  salt.  Mr.  Perkins,  therefore,  tried 
several  experiments  of  this  sort  with  cylinders  of  brass 
and  iron,  constructed  for  the  purpose.  The  result  of 
these  trials  established  the  fact  of  the  compressibility  of 
water  in  the  most  satisfactory  manner.  30,000  pounds 
pressure  to  the  inch  will  lessen  its  bulk  one  twelfth. 

Fluids  have  weight,  and  gravitate  towards  the  earth, 
according  to  their  density,  in  the  same  way  that  solids 
do ;  but,  from  the  want  of  cohesion  among  their  par- 
ticles, they  are  incapable  of  assuming  any  particular 
form  without  assistance,  and,  consequently,  they  always 
take  the  shape  of  the  vessel  which  contains  them. 
They  also  exert  a  certain  force  against  the  sides  of 
that  vessel,  from  their  tendency  to  fall,  which  consti- 
tutes their  lateral  pressure ;  for  fluids  not  only  press 
downwards  with  their  whole  might,  in  obedience  to 
gravitation,  but  they  press  sideways,  or  laterally,  in  all 
directions  at  the  same  time,  and  from  the  same  cause ; 
and  consequently,  no  fluid  can  remain  in  a  state  of 
quiet  equilibrium  unless  every  part  of  its  surface  is 
equidistant  from  the  centre  of  the  earth,  or  in  what  is 
generally  called  a  level  plane,  though  that  apparent 
plane  is,  in  fact,  not  a  plane,  but  partakes  of  the  con- 
vexity of  the  earth.  And  it  is  for  the  purpose  of  es- 
tablishing such  an  equilibrium  that  fluids  always  run 
from  a  higher  to  a  lower  situation. 

For  the  purpose  of  explaining  the  manner  in  which 
the  surfaces  of  fluids  become  level,  it  may  be  very 
fairly  supposed  that  the  particles  of  which  they  are 
composed  are  placed  one  upon  another,  so  as  to  form 
what  may  be  termed  pillars  or  columns  of  particles ; 
and  supposing  all  the  particles  to  be  of  the  same  size 
9* 


102  HYDROSTATICS. 

and  weight,  the  columns  on  one  side  of  the  vessel  will 
be  an  exact  balance  to  those  on  the  other  side.  The 
cause  of  bodies  floating  upon  fluids,  or  sinking  in  them, 
may  be  explained  the  same  way  ;  for,  whenever  a  solid 
is  immersed  in  a  fluid,  it  displaces  a  quantity  of  water, 
and  consequently  renders  the  columns  of  particles 
underneath  it  shorter,  and,  therefore,  lighter,  than  those 
which  surround  it.  But  the  weight  of  the  floating 
body  becomes  a  counterpoise  to  the  greater  length  of 
the  surrounding  columns,  and  must  in  every  case  be 
precisely  equal  to  the  quantity  of  water  which  it  dis- 
places. Consequently,  all  things  which  are  lighter  than 
their  own  bulk  of  water  will  swim,  and  all  that  are 
heavier  must  sink.  A  ship,  therefore,  of  500  tons' 
burden  must  displace  500  tons  of  water  from  the  bed, 
or  hollow,  which  it  makes  from  the  keel  up  to  the 
water  line ;  and  in  this  way  the  actual  tonnage  of  a 
ship  is  estimated,  although  her  nominal  burden  is  fixed 
by  another  species  of  measurement. 

The  truth  of  this  position  is  very  satisfactorily  proved 
by  putting  the  model  of  a  ship  into  a  scale,  and  ex- 
actly balancing  it  with  water  in  the  other  scale.  The 
ship  is  then  removed,  and  placed  in  a  small  cistern 
quite  filled  with  water,  when  a  quantity  of  it  will  flow 
over,  and,  on  taking  the  ship  out,  it  will  be  found  that 
the  vacuity  will  be  exactly  filled  by  the  water  in  the 
scale,  being  the  weight  of  the  floating  body. 

Notwithstanding  the  above  experiments  seem  to 
prove  that  the  pressures  of  fluids  are  in  consequence 
of  a  mechanical  equilibrium,  dependent  upon  the 
gravitation  of  equal  quantities  of  matter  acting  against 
each  other,  yet,  on  more  mature  examination,  it  is 


HYDROSTATICS.  103 

found  that  such  pressures  are  regulated  by  perpen- 
dicular height, 'and  the  area  of  the  surface  acted  upon, 
without  any  regard  to  quantity,  or  absolute  gravity. 
For,  although  a  pound  of  water  can,  in  itself,  produce 
no  greater  effect  than  is  due  to  a  pound,  yet,  from  the 
properties  of  fluids,  it  may  be  so  disposed  as  to  pro- 
duce the  effect  of  many  hundred  pounds.  This  has 
obtained  the  name  of  the  hydrostatic  paradox.  The 
bottom  of  a  vessel  bears  a  pressure  proportional  to  the 
height  of  the  liquid ;  so  likewise  do  those  parts  of  the 
sides  which  are  contiguous  to  the  bottom,  because  the 
pressure  of  fluids  is  equal  every  way.  Thus  the  sides 
of  a  vessel  must  every  where  sustain  a  pressure  pro- 
portional to  their  distance  from  the  upper  surface  of 
the  liquid  ;  whence  it  follows  that,  in  a  vessel  full  of  a 
liquid,  the  sides  bear  the  greatest  stress  in  those  parts 
next  the  bottom,  and  the  stress  upon  the  sides  de- 
creases with  the  increase  of  the  distance  from  the 
bottom,  and  in  the  same  proportion ;  so  that,  in  vessels 
of  considerable  height,  the  lower  parts  ought  to  be 
much  stronger  than  the  upper.  This  has  been  illus- 
trated by  a  striking  experiment  A  strong,  though 
small,  tube  of  tin,  twenty  feet  high,  was  inserted  in  the 
bung-hole  of  a  hogshead :  water  was  poured  in  till  it 
rose  within  a  foot  of  the  top  of  the  tube ;  the  hogshead 
then  burst,  and  the  water  was  scattered  about  with 
incredible  force. 

The  running,  or  spouting  of  fluids,  from  the  sides  of 
vessels,  arises,  likewise,  from  lateral  pressure,  and  is, 
consequently,  influenced  by  the  height  of  the  column, 
without  regard  to  the  quantity  it  contains  :  consequently, 
if  any  given  quantity  of  water  issues  in  a  certain  time 


104  HYDROSTATICS. 

from  a  hole  in  a  cask,  or  reservoir,  double  that  quanti- 
ty will  issue  from  another  hole,  of  precisely  the  same 
dimensions,  if  it  be  situated  four  times  as  deep  as  the 
first,  below  the  surface  of  the  fluid.  A  similar  hole, 
nine  times  as  deep,  will  deliver  three  times  as  much 
fluid  in  the  same  time.  The  discharge  is,  therefore, 
as  the  square  root  of  the  depth  beneath  the  surface ; 
which  law  is  of  great  importance  in  the  practical  con- 
struction and  arrangement  of  water-works,  and,  if  not 
attended  to,  may  occasion  a  great  waste  of  power. 

From  the  principles  already  advanced,  it  follows  that 
a  stream  will  always  rise  as  high  as  its  fountain-head : 
that  is,  if  a  tube,  twenty  miles  long,  and  rising  and 
descending  among  the  inequalities  of  the  land,  were 
nearly  filled  with  water,  and  could  have  its  ends  brought 
together  for  comparison,  it  would  exhibit  two  liquid 
surfaces,  having  precisely  the  same  level,  and,  on  either 
end  being  raised,  the  fluid  would  sink  in  it,  to  rise  in 
the  other.  If  there  were  two  lakes,  on  adjoining  hills, 
of  different  heights,  a  pipe  of  communication  descend- 
ing across  the  valley,  and  connecting  them,  would  soon 
bring  them  to  the  same  level ;  or,-  if  one  were  much 
lower  than  the  other,  it  would  empty  the  latter  into  the 
former.  The  ancient  method  of  supplying  cities  with 
water  was  by  means  of  aqueducts,  or  bridges,  built 
over  the  valleys,  and  supporting  either  pipes,  or  a  con- 
duit, or  channel.  These  stupendous  and  costly  erec- 
tions, the  remains  of  which  still  adorn  the  ruins  of 
ancient  cities,  are  supposed  to  have  owed  their  origin 
to  an  ignorance  of  the  above  principle  of  hydrostatics ; 
but  it  is  quite  as  probable  that  the  ancients  were  com- 
pelled to  erect  these  structures  by  the  practical  difficulty 


HYDROSTATICS.  105 

of  uniting  a  long  range  of  pipes  in  such  a  manner  as  to 
remain  perfectly  water-tight  against  the  pressure  of  a 
heavy  column  of  water.  This  is  not  easy  even  in 
the  present  improved  state  of  the  mechanic  arts,  and 
with  all  the  advantage  of  cast-iron  and  the  most 
durable  materials,  instead  of  stone  and  earthenware, 
which  appear  to  have  been  chiefly  used  for  pipes  in 
the  construction  of  the  older  water-works.  Even  at 
the  present  day,  it  is  found  more  convenient  to  conduct 
water  to  cities,  from  long  distances,  by  open  aqueducts 
than  by  pipes,  as  has  been  done  at  New  York.  Here  the 
purest  water  is  conveyed  from  the  River  Croton,  which 
is  forty-one  miles  from  the  city,  to  a  reservoir  which 
will  hold  150,000,000  gallons.  From  this  reservoir,  it 
is  carried  by  pipes  to  all  parts  of  the  city,  in  sufficient 
quantities  to  supply  every  demand  for  it,  for  domestic 
uses,  for  watering  streets,  and  extinguishing  fires. 

What  has  been  said  upon  water-works  equally  ap- 
plies to  fountains ;  for  a  jet  can  be  produced  only  by  the 
effort  of  water  to  rise  to  its  level,  or  by  its  being  under 
the  influence  of  condensed  air,  or  some  other  force. 
Thus,  if  an  elevated  cistern,  or  reservoir,  be  kept  sup- 
plied with  water,  and  a  tube  descends  from  its  lower 
part,  ending  in  a  small  orifice  pointing  upwards,  the 
water  will  spout  from  it,  and  form  a  jet  nearly  equal  in 
height  to  that  of  the  water  from  which  it  is  supplied ; 
but,  for  want  of  that  support  which  the  fluid  derives 
from  the  sides  of  a  tube,  or  close  vessel,  and  from  its 
being  in  constant  and  rapid  motion  through  the  resisting 
air,  it  will  never  gain  the  full  height  of  the  column  of 
supply. 

Since  the  weight  which  a  body  loses,  when  immersed 


106  HYDROSTATICS. 

in  a  fluid,  is  always  the  weight  of  as  much  of  that  fluid 
as  is  equal  in  bulk  to  itself,  it  follows  that  the  weight 
lost  by  the  body  cannot  at  all  depend  either  on  the 
depth  of  the  fluid  itself,  or  the  depth  to  which  the  body 
is  immersed.  An  anchor  loses  no  more  of  its  weight 
when  it  is  at  the  bottom,  than  when  it  is  just  below  the 
surface ;  for  in  both  cases  it  loses  the  weight  of  as  much 
water  as  is  equal  in  bulk  to  itself.  It  is  not  easier  to 
swim  in  deep  than  in  shallow  water ;  for  whatever  is  the 
depth,  a  man  loses  the  weight  of  as  much  water  as  is 
equal  in  bulk  to  his  own  body ;  for  which  reason,  shal- 
low water  will  buoy  him  up  with  as  great  force  as  deep 
water.  Indeed,  it  is  easier  to  swim  in  the  sea  than  in 
a  river,  because  salt  water  is  specifically  heavier  than 
fresh.  In  the  Dead  Sea,  the  water  of  which  is  more 
deeply  saturated  with  salt  than  any  other  body  of  water 
in  the  world,  this  principle  is  strikingly  illustrated.  In 
the  Travels  of  Mr.  Stephens  is  the  following  account  of 
his  attempting  to  swim  in  this  lake  :  "  I  know,  in  refer- 
ence to  my  own  specific  gravity,  that,  in  the  Atlantic  or 
Mediterranean,  I  cannot  float  without  some  little  move- 
ment of  the  hands,  and  even  then,  my  body  is  almost 
totally  submerged;  but  here,  when  I  threw  myself 
upon  my  back,  my  body  was  half  out  of  water.  It 
was  an  exertion  even  for  my  lank  Arabs  to  keep  them- 
selves under.  When  I  struck  out,  in  swimming,  it  was 
exceedingly  awkward  ;  for  my  legs  were  constantly  ris- 
ing to  the  surface,  and  even  above  the  water.  I  could 
have  lain  there  and  read,  with  perfect  ease.  In  fact,  I 
could  have  slept." 

There  are  few,  if  any,  animals  that  are  specifically 
heavier  than  common  water.     The  substances,  indeed, 


HYDROSTATICS.  107 

of  both  animals  and  vegetables,  are  specifically  heavier ; 
the  floating  of  either  is,  therefore,  to  be  attributed  to 
the  cells,  or  receptacles,  interspersed  within  them, 
which  are  filled  with  air,  oil,  and  substances  lighter ; 
so  that,  taken  together,  they  form  a  mass  specifically 
lighter  than  common  water.  Thus  the  bulk  of  the 
body  is  increased  by  distending  the  chest  in  inspira- 
tion ;  this  has  been  tried  by  an  experiment  on  a  fat 
man,  of  an  ordinary  size,  by  finding  what  weight  he 
could  support,  so  as  to  have  the  top  of  the  head  just 
above  water.  When  his  lungs  were  full  of  air,  Ihe 
was  found  to  rise  with  fourteen  pounds  of  lead ;  but 
on  breathing  out  the  air,  he  could  sustain  only  eleven 
pounds. 

To  show  the  practical  purposes  the  principle  here 
illustrated  may  serve,  we  will  relate  the  story  of  Hiero7s 
crown.  Hiero,  king  of  Syracuse,  had  delivered  a 
certain  weight  of  gold  to  a  workman,  to  be  made  into  a 
crown ;  the  latter  brought  back  a  crown  of  the  proper 
weight,  which  was  afterwards  suspected  to  be  alloyed 
with  silver.  The  king  applied  to  the  celebrated  math- 
ematician, Archimedes,  to  know  how  he  might  detect 
the  cheat,  the  difficulty  being  to  measure  the  bulk  of 
the  crown,  without  melting  it  into  a  regular  figure : 
silver  being,  weight  for  weight,  of  greater  bulk  than 
gold,  any  alloy  of  the  former,  in  place  of  an  equal 
weight  of  the  latter,  would  mechanically  increase  the 
bulk  of  the  crown.  Archimedes  was.  at  first  embar- 
rassed with  this  problem ;  but  one  day,  on  going  into  a 
bath,  which  happened  to  be  quite  filled  with  water,  he 
was  struck  with  the  simple  fact  that  a  quantity  of  water, 
of  the  same  bulk  as  his  body,  must  flow  over  before  he 


108 


HYDROSTATICS. 


could  immerse  himself.  It  immediately  occurred  to 
him  that,  by  immersing  a  weight  of  pure  gold,  equal 
to  that  which  the  crown  ought  to  have  contained,  in  a 
vessel  full  of  water,  and  observing  how  much  water 
was  left  when  the  gold  was  taken  out,  and  by  after- 
wards doing  the  same  thing  with  the  crown  itself,  he 
could  ascertain  whether  the  latter  exceeded  the  former 
in  bulk.  The  moment  he  was  struck  with  this  thought, 
his  exultation  was  so  great  that  he  leaped  out  of  the 
bath,  and,  without  stopping  to  put  on  his  clothes,  ran 
home,  crying  out,  "  Eureka  !  "  "  I  have  found  it ! "  an 
expression  which  has  become  proverbial. 


HYDRAULICS. 


-^^    ^ifeti-* 


WATER,  as  we  have  already  remarked,  may  be 
made  a  useful  agent  of  power,  merely  by  allowing  it  to 
act  with  the  force  of  its  own  gravity,  as  in  turning  a  mill ; 
and  in  this  manner  it  is  extensively  employed  in  all 
civilized  countries  possessing  streams  which  are  suf- 

30H.— 10 


110  HYDRAULICS. 

ficiently  rapid  in  their  descent.  But  water  may  be 
rendered  otherwise  useful  as  an  agent  of  force  in  the 
arts.  Although  subtile  in  substance,  and -eluding  the 
grasp  of  those  who  attempt  to  handle  it,  water  can, 
without  alteration  of  temperature,  be  made  to  act,  as  a 
mechanical  power,  as  conveniently  and  usefully  as  if 
it  were  a  solid  substance,  like  iron,  stone,  or  wood. 
The  lever,  the  screw,  the  inclined  plane,  or  any  of  the 
ordinary  mechanical  powers,  are  not  more  remarkable 
as  instruments  of  force  than  water,  a  single  gallon  of 
which  may  be  made  to  perform  what  cannot  be  ac- 
complished, except  at  enormous  cost  and  labor,  by  the 
strongest  metal. 

To  render  water  serviceable  as  an  instrument  of 
force,  it  must  be  confined,  and  an  attempt  then  be  made 
to  compress  it  into  less  than  its  natural  bulk.  In 
making  this  attempt,  the  impressed  force  is  freely  com- 
municated through  the  mass,  and,  in  the  endeavor  to 
avoid  compression,  the  liquid  will  repel  whatever  mova- 
ble object  is  presented  to  it.  The  force  with  which 
water  may  be  squirted  from  a  boy's  syringe  gives  but 
a  feeble  idea  of  the  power  of  liquids,  when  subjected, 
in  a  state  of  confinement,  to  the  impression  of  exter- 
nal force. 

We  have  already  spoken  of  the  tendency  of  water 
to  seek  every  where  a  common  level,  on  the  principle 
of  which  aqueducts  are  constructed.  Springs  in  the 
ground  are  natural  hydraulic  operations,  and  are  ac- 
counted for  on  principles  connected  with  the  laws  of 
fluids.  One  class  of  springs  is  caused  by  capillary  at- 
traction, or  natural  attractive  forces,  by  which  liquids 
rise  in  small  tubes,  porous  substances,  or  between  flat 


Ill 

bodies,  closely  laid  together.  This  species  of  power 
is  a  remarkable  variety  of  the  mutual  attraction  of 
matter,  and  is  as  unaccountable  as  the  attraction  of 
gravitation,  or  the  attraction  exercised  by  the  load- 
stone. Springs  from  capillary  attraction  are  believed 
to  be  less  common,  and  of  less  importance,  than  springs 
which  originate  from  the  obvious  cause  of  water  find- 
ing its  level.  The  water  which  falls  in  the  form  of 
rain  sinks  into  the  ground  in  high  situations,  and  finds 
an  outlet  at  a  lower  level,  though  perhaps  at  a  con- 
siderable distance. 

The  friction,  or  resistance,  which  fluids  suffer  when 
passing  through  pipes,  is  much  greater  than  might  be 
expected.  It  depends  chiefly  upon  the  particles  being 
constantly  driven  from  their  direct  course  by  the  irregu- 
larities in  the  surface  of  the  pipe.  An  inch  tube,  of 
200  feet  in  length,  placed  horizontally,  is  found  to  dis- 
charge only  a  fourth  part  of  the  water  which  escapes 
by  a  simple  aperture.  Air,  likewise,  in  passing  through 
tubes,  is  retarded,  as  was  discovered  by  a  person  who 
construct*  4  a  great  bellows  at  a  waterfall,  to  blow  a 
furnace  two  miles  off.  This  resistance  is  so  great,  that 
when  it  was  first  proposed  to  lay  gas-pipes  in  England, 
some  engineers  were  of  opinion  that  the  gas  could  not 
be  forced  through  them.  All  liquids  flow  faster  through 
an  orifice,  or  pipe,  the  higher  their  temperature  is 
kept,  as  this  diminishes  that  cohesion  of  parts  which 
exists,  to  a  certain  degree,  in  all  of  them,  and  affects  so 
much  their  internal  movements.  The  flux  of  water 
through  orifices,  under  uniform  circumstances,  is  so 
regular,  that,  before  the  invention  of  clocks  and  watches, 
it  was  employed  as  a  means  of  measuring  time.  These 


1 12  HYDRAULICS. 

water-clocks  were  called  clepsydra,  and  were  often 
used  by  ancient  orators,  to  show  them  when  the  time 
allotted  to  them  for  speaking  had  expired.  The  com- 
mon hour-glass  of  running  sand  is  another  modification 
of  the  same  principle. 

The  progress  of  water,  in  an  open  conduit,  such  as 
the  channel  of  a  river,  or  an  aqueduct,  is  influenced  by 
friction  in  the  same  manner.  But  for  this,  and  the 
effect  of  bending,  a  river,  like  the  Rhone,  drawing  its 
waters  from  an  elevation  of  a  thousand  feet  above  the 
level  of  the  ocean,  would  pour  them  out  with  the  ve- 
locity of  water  issuing  from  the  bottom  of  a  reservoir 
a  thousand  feet  deep ;  that  is  to  say,  at  the  rate  of  170 
miles  an  hour.  The  ordinary  flow  of  rivers  is  about 
3  miles  an  hour,  and  their  channels  slope  three  or 
four  inches  a  mile.  Three  feet  fall,  a  mile,  makes  a 
mountain  torrent.  The  friction  of  water,  moving  in 
water,  is  such,  that  a  small  stream  directed  through  a 
pool,  and  rapid  enough  to  rise  over  the  opposite  bank, 
will  soon  empty  the  pool.  Large  fenny  tracts  have 
been  drained  in  this  manner.  The  friction  between 
air  and  water  is  also  singularly  strong,  as  is  proved,  on 
a  great  scale,  by  the  magnitude  of  the  ocean  waves 
which  are  caused  by  it.  A  little  oil,  thrown  upon  the 
surface  of  the  water,  spreads  as  a  thin  film  all  over  it, 
and  defends  it  from  further  contact  and  friction  of  air. 
If  this  is  done  at  the  windward  side  of  a  pond,  where 
the  waves  begin,  the  whole  surface  will  soon  become 
as  smooth  as  glass ;  and  even  out  at  sea,  where  the 
commencement  of  the  waves  cannot  be  reached,  oil 
thrown  upon  them  smooths  their  surface,  and  prevents 
their  curling  over  and  breaking. 


HTDRAITCJCS.  113 

A  stone  thrown  into  a  smooth  pond  causes  a  suc- 
cession of  circular  waves  to  spread  from  the  spot 
where  it  falls.  They  become  of  less  elevation  as  they 
expand,  and  each  new  one  is  less  raised  than  the 
preceding,  so  that  gradually  the  liquid  mirror  is  again 
as  perfect  as  before.  Several  stones  falling  at  the 
same  time  in  different  places  cause  crossing  circles, 
which,  however,  do  not  check  the  progress  of  each 
other  —  a  phenomenon  seen  hi  beautiful  miniature  at 
each  leap  of  the  little  insects  which  cover  the  surfaces 
of  ponds  in  the  calm  days  of  summer.  Such  waves 
are  caused  in  this  manner :  When  the  stone  falls  into 
the  water,  because  the  liquid  is  incompressible,  a  part 
of  it  is  displaced  laterally,  and  becomes  an  elevation,  or 
circular  wave,  around  the  stone ;  this  wave  then  falls 
downward  and  outward,  in  obedience  to  the  laws  of 
fluidity,  and  the  circle  is  seen  to  spread.  In  the  mean- 
time, where  the  stone  descended,  a  hollow  is  left  for  a 
moment  in  the  water,  but,  owing  to  the  surrounding 
pressure,  it  is  soon  filled  up  by  a  sudden  rush  from 
below.  The  rising  water  does  not  stop,  however,  at  the 
exact  level  of  that  around,  but,  like  a  pendulum,  sweep- 
ing past  the  centre  of  its  arc,  it  rises  as  far  above  the 
level  as  the  depression  was  deep.  This  central  eleva- 
tion now  acts  as  the  stone  did  originally,  and  causes  a 
second  wave,  which  pursues  the  first,  and,  when  the 
centre  subsides,  like  the  pendulum  still,  it  sinks  again 
as  much  below  the  level  as  it  had  mounted  above ; 
hence  it  must  again  rise,  again  to  fall,  and  this  for 
many  times,  sending  forth  a  new  wave  at  each  alterna- 
tion. Owing  to  the  friction  among  the  particles  of 
H  10* 


114  HYDRAULICS. 

water,  each  new  wave  is  less  raised  than  the  preceding, 
and  at  last  the  appearance  dies  away. 

The  common  cause  of  waves  is  the  friction  of  the 
wind  upon  the  surface  of  the  water.  Little  ridges, 
or  elevations,  first  appear,  which,  by  the  continuance 
of  the  force,  gradually  increase  till  they  become 
rolling  billows.  The  heaving  of  the  Bay  of  Biscay, 
or,  still  more  remarkably,  that  of  the  open  ocean 
between  the  southern  capes  of  America  and  Africa, 
exhibits  one  extreme,  and  the  stillness  of  the  tropical 
seas,  which  are  sheltered  by  encircling  land,  exhibits 
the  other.  In  sailing  round  the  Cape  of  Good  Hope, 
waves  are  met  with  so  vast,  that  a  few  ridges  and 
depressions  occupy  the  extent  of  a  mile.  But  these 
are  not  so  dangerous  to  a  ship  as  a  shorter  sea,  with 
more  perpendicular  waves.  The  slope  in  the  former 
is  so  gentle,lhat  the  rising  and  falling  are  scarcely  felt, 
while  the  latter,  causing  an  abrupt  and  violent  pitching 
of  the  vessel,  are  often  destructive.  The  unfortunate 
steam-ship  President  doubtless  perished  from  this  cause. 
She  encountered  a  tremendous  gale  on  the  day  after 
leaving  New  York,  and,  during  the  height  of  its  fury, 
she  must  have  been  at  a  point  where  the  Gulf  Stream 
approaches  the  shoal  called  George's  Bank,  and  causes 
an  almost  perpendicular  surge  of  the  most  dangerous 
character.  The  ship  was  last  seen  struggling  ahead 
directly  against  the  sea,  and  pitching  violently.  Her 
enormous  length  must  have  greatly  added  to  the  danger, 
and  probably  caused  her  soon  to  rack  to  pieces. 

The  velocity  of  waves  is  in  proportion  to  their  mag- 
nitude.   The  largest  waves  move  from  thirty  to  forty 


flYDRAOTJCS.  115 

miles  an  hour.  It  is  a  vulgar  belief  that  the  water 
itself  advances  with  the  speed  of  the  wave,  whereas  it 
is  only  the/ora  that  advances,  while  the  substance, 
with  the  exception  of  a  little  spray  above  it,  remains 
rising  and  falling  in  the  same  place,  with  the  regularity 
of  a  pendulum.  A  wave  of  water,  in  this  respect,  is 
exactly  imitated  by  the'  wave  running  along  a  stretched 
rope  when  one  end  is  shaken,  or  by  the  mimic  waves 
of  our  theatres,  which  are  generally  undulations  of 
cloth  shaken  up  and  down.  But  when  a  wave  reaches 
a  shoal,  or  beach,  the  water  becomes  really  progressive, 
because  then,  as  it  cannot  sink  directly  downwards,  it 
falls  over  and  forwards,  seeking  its  level. 

So  terrific  is  the  spectacle  of  a  storm  at  sea,  that  it 
is  generally  viewed  through  a  medium  which  biases 
the  judgment ;  and,  lofty  as  waves  really  are,  imagina- 
tion pictures  them  loftier  still.  Now,  no  wave  rises 
more  than  ten  feet  above  the  ordinary  sea  level,  which, 
with  the  ten  feet  that  it  afterwards  descends  below  it, 
give  twenty  feet,  from  the  hollow,  or  trough,  of  the  sea, 
as  the  sailors  call  it,  to  the  adjoining  summit  The 
spray  of  the  sea,  driven  along  by  the  violence  of  the 
wind,  is,  of  course,  much  higher  than  the  crest  of  the 
wave,  and  a  wave  coming  against  an  obstacle  may 
dash  to  a  great  elevation  above  it.  At  the  Eddystone 
lighthouse,  in  the  English  Channel,  in  heavy  storms, 
the  waves  dash  over  the  top  of  the  lantern. 

On  a  superficial  view  of  the  doctrine  of  resistance, 
in  the  case  of  bodies  moving  through  a  fluid,  many 
persons  would  conclude  that,  if  a  body  moving  through 
the  water  at  a  given  rate,  meets  a  given  resistance,  it 
should  encounter  double  that  resistance  when  moving 


116  HYDRAULICS. 

at  double  the  rate  ;  but  this  is  a  fallacy  ;  the  resistance 
is  four  times  greater  with  a  double  rate.  The  reason 
is  very  clear.  A  boat  which  moves  one  mile  an  hour 
displaces  a  certain  quantity  of  water,  and  with  a  cer- 
tain velocity ;  if  it  moves  twice  as  fast,  it  of  course 
displaces  twice  as  many  particles  in  the  same  time, 
and  requires  to  be  moved  with  twice  the  force  on  that 
account.  But  it  also  displaces  every  particle  with  a 
double  velocity,  and  requires  another  doubling  of  the 
power  on  this  account;  the  power  therefore,  being 
doubled  on  two  accounts,  becomes  a  power  of  four. 
In  the  same  manner,  with  a  triple  speed,  three  times  as 
many  particles  are  moved,  and  each  particle  with  a 
triple  velocity;  therefore,  a  force  of  nine  must  be 
applied  to  overcome  the  resistance.  For  a  speed  of 
four,  sixteen  is  wanted,  and  so  on.  Thus,  even  if 
the  resistance  against  the  bow  of  the  vessel  only  were 
considered,  one  hundred  horses  would  drag  a  canal- 
boat  only  ten  times  faster  than  one  horse.  But  there  is 
another  important  element  in  the  calculation  —  namely, 
the  lessening  of  the  usual  water-pressure  on  the  stern 
of  the  vessel  as  she  moves  forward,  on  account  of 
which,  the  force  required  to  produce  an  increased 
velocity  is  still  greater  than  what  is  shown  by  the 
above  calculation. 

There  is  not  a  more  important  truth  in  physics  than 
this  ;  it  explains  so  many  phenomena  of  nature,  and 
becomes  a  guide  in  so  many  matters  of  art.  It  ex- 
plains in  what  manner  so  great  an  expenditure  of  fuel 
is  required  to  obtain  high  velocities  in  steamboats.  It 
shows  the  folly  of  crowding  sail  upon  a  ship  with  a 
strong  breeze,  the  trifling  advantage  in  point  of  speed 


HYDRAULICS.  117 

by  no  means  compensating  for  the  wear  of  the  sails 
and  the  risk  of  accidents.  No  seamen  practise  this  so 
much  as  the  Americans,  who  are  ready  to  incur  any 
degree  of  expense,  and  run  any  risk,  in  the  hope  of 
gaining  a  little  time.  We  remember  an  instance  where 
a  Boston  merchant  said  to  one  of  his  shipmasters  about 
to  sail,  "  Wear  out  what  you  please,  but  make  a  quick 
passage." — This  ship  returned  from  Europe,  having 
worn  out  an  entire  new  set  of  sails  in  one  voyage. 
The  above  law  explains,  also,  why  a  ship  glides  through 
the  water  one  or  two  miles  an  hour  with  very  little  wind, 
although,  with  a  powerful  breeze,  she  would  sail  only 
eight  or  ten.  Less  than  the  100th  part  of  that  force 
of  wind  which  drives  her  ten  miles  an  hour  will 
drive  her  one  mile ;  and  less  than  the  400th  part  will 
drive  her  half  a  mile.  Thus,  also,  during  a  calm,  a 
few  men  pulling  in  a  boat  can  tow  a  large  ship. 

If  a  ship  be  anchored  in  a  stream  where  the  current 
is  four  miles  an  hour,  the  strain  on  her  cable  is  not 
one  fourth  part  so  great  as  if  the  current  were  eight 
miles.  The  rapid  increase  of  resistance,  in  proportion 
to  the  increase  of  velocity,  shows  that  we  soon  reach 
the  maximum  of  speed  in  ships.  Fifteen  miles  an  hour 
is  the  utmost  that  a  ship  can  sail.  No  fish  swims  faster 
than  twenty  miles  an  hour.  The  flight  of  birds,  also, 
has  a  limited  celerity ;  but  as  the  thin  air  opposes 
much  less  resistance  than  water,  flying  is,  of  course, 
more  rapid  than  sailing  or  swimming.  The  crow, 
when  flying  homeward  against  the  storm,  cannot  face 
the  wind  in  the  open  sky,  but  skims  along  the  surface 
of  the  earth  in  deep  valleys,  and  wherever  the  swift- 
ness of  the  wind  is  retarded  by  terrestrial  obstacles. 


118 


HYDRAULICS. 


The  great  albatross  can  stem  upon  the  wing  the  cur- 
rent  of  a  gale,  keeping  company  with  a  driving  ship 
when  the  wind  is  passing  at  the  rate  of  a  hundred 
miles  an  hour ;  but  perhaps  this  is  the  limit  to  which 
winged  speed  can  reach. 

If  a  flat  surface  experience  a  certain  resistance,  a 
projecting  surface,  like  that  of  a  ball  or  wedge,  is 
resisted  in  a  less  degree.  The  explanation  is,  that  a 
flat  surface  throws  the  particles  of  fluid  almost  directly 
outwards  from  its  centre  to  its  circumference  ;  but  the 
convex  or  wedge-like  surface,  while  displacing  them 
just  as  far,  does  it  more  slowly,  and  therefore  with  less 
expenditure  of  force  in  proportion  as  its  point  is  in 
advance  of  its  shoulder,  or  broadest  part.  The  shape 
of  the  hinder  part  of  a  solid  moving  through  a  fluid  is 
of  importance,  for  corresponding  reasons.  Fishes  are 
wedge-like  both  before  and  behind  :  so  are  birds,  and 
they  stretch  out  their  necks  while  flying,  so  as  to  be- 
come like  sharp  points  dividing  the  air.  In  the  form 
of  the  under  part  of  boats  and  ships,  men  have  imitated 
the  shape  of  fishes.  There  are  boats  used  by  the 
Chinese  called  snake-boats,  which  are  only  a  foot  or 
two  in  width,  but  a  hundred  feet  long,  and  when  rowed, 
as  they  often  are,  by  a  hundred  oars,  their  swiftness  is 
excessive.  Oars  for  boats  are  made  flat,  and  often  a 
little  concave,  that  the  mutual  action  between  them 
and  water  may  be  as  great  as  possible.  The  webbed 
feet  of  water-fowl  are  oars ;  in  advancing,  they  col- 
lapse, like  a  shutting  umbrella,  but  open  outwards  in 
the  thrust  backward,  so  as  to  offer  a  broad  concave 
surface  to  the  water.  The  expanded  wings  of  birds 
are,  in  like  manner,  a  little  concave  towards  the  air 


HYDRAULICS.  119 

which  they  strike.  The  sails  of  ships,  when  they  are 
receiving  a  fair  wind,  are  left  slack,  so  as  to  swell  and 
become  hollow. 

We  conclude  this  topic  by  the  following  striking 
example  of  the  power  of  water,  given  by  Mr.  Olm- 
stead :  "  A  waterfall  like  that  of  Niagara,  where  an 
immense  body  of  water  rolls  first  in  rapids  down  a 
long  inclined  plane,  and  then  descends  perpendicularly 
from  a  great  height,  affords  one  of  the  greatest  ex- 
hibitions of  mechanical  power  ever  seen.  The  Falls 
of  Niagara  contain  power  enough  to  turn  all  the  mills 
and  machines  in  the  world.  They  waste  a  greater 
amount  of  power  every  minute  than  was  expended  in 
building  the  pyramids  of  Egypt ;  for,  in  that  short 
space  of  time,  millions  of  pounds  of  water  go  over 
the  falls,  and  each  pound,  by  the  velocity  it  gains  in 
first  falling  down  the  rapids,  and  then  perpendicularly, 
acquires  resistless  energy.  Water  falling  one  hundred 
feet  would  strike  on  every  square  foot  with  a  force  of 
more  than  six  thousand  pounds." 


PNEUMATICS; 

OR, 

THE  MECHANICAL  PROPERTIES  OF  AIR. 


THE  earth  which  we  inhabit  is  entirely  enveloped,  or 
surrounded,  by  a  thin,  transparent,  and  invisible  fluid, 
called  air.  This  air,  together  with  the  various  gases, 
steams,  vapors,  and  exhalations  that  are  constantly 
thrown  into  it,  and  which  form  clouds,  is  called  by 
the  general  name  of  the  atmosphere.  Consequently, 
atmospheric  air  is  of  a  very  mixed  nature  ;  but  when 
pure,  it  is  found,  by  chemical  examination,  to  consist  of 
two  permanently  elastic  gases,  or  airs,  called  nitrogen 


FNEUMATICS.  121 

and  oxygen,  as  we  shall  hereafter  show  in  our  chapter 
on  Chemistry. 

Air,  though  invisible,  is  a  material  substance,  and 
partakes  of  all  the  properties  which  belong  in  com- 
mon to  other  matter ;  for  it  occupies  space,  attracts 
and  is  attracted,  and,  consequently,  has  weight.  It 
likewise  partakes  of  the  nature  of  fluids,  for  it  adapts 
itself  to  the  form  of  the  vessel  which  contains  it ;  and 
it  presses  equally  in  all  directions ;  consequently,  it  must 
be  considered  as  a  material  fluid.  But,  inasmuch  as  it 
is  highly  elastic,  a  property  which  is  common  to  all 
gases,  steams,  and  vapors,  while  the  more  visible  and 
tangible  fluids,  such  as  water,  oil,  spirits,  &c.,  possess 
this  character  in  a  very  slight  degree,  if  at  all,  so  they 
require  a  separate  examination. 

The  various  airs,  or  gases,  are  called  permanently 
elastic,  because,  under  all  changes  which  can  be 
wrought  upon  them,  they  maintain  their  characters  of 
fluidity  and  elasticity,  and  will  not  admit  of  being  con- 
gealed, or  rendered  solid.  With  steams  and  vapors,  the 
case  is  very  different;  for  they  arise  from  inelastic 
fluids  by  the  application  of  heat,  and  they  are  highly 
elastic  so  long  as  they  retain  their  form  of  vapor ;  but 
on  being  cooled,  they  return  again  to  their  original 
state  of  inelastic  fluid,  and  therefore  differ  very  ma- 
terially from  air,  and  cannot  be  said  to  be  permanently 
elastic.  Water  affords  a  very  good  instance,  for  this 
is  inelastic ;  but  its  steam  is  elastic  in  the  highest 
degree ;  whenever  this  steam  becomes  cooled,  it 
reverts  back  into  its  original  state  of  water,  and  of 
course  resumes  all  its  former  characters. 

Since  air  has  weight,  and  every  thing  upon  the  earth 

XIII.— 11 


122  PNEUMATICS. 

is  surrounded  by  it,  it  follows  that  all  things  must  be 
subject  to  the  pressure  which  will  be  exerted,  not  only 
upon  them,  but  upon  itself;  and  since  air  is  elastic,  or 
capable  of  yielding  to  pressure,  so,  of  course,  the  lower 
part  of  the  atmosphere  will  be  more  dense,  or  in  a 
state  of  greater  compression,  than  that  which  is  above. 
Suppose,  for  example,  that  the  whole  haight  of  the 
atmosphere  is  divided  into  100  equal  parts,  and  that 
each  of  these  may  weigh  an  ounce,  or  may  be  equiv- 
alent to  the  production  of  that  pressure ;  then  the  earth, 
and  all  things  upon  its  surface,  will  be  pressed  with  the 
whole  100  ounces ;  the  lowest  stratum  of  air  will  be 
pressed  by  the  99  ounces  above  it,  the  next  by  98,  and 
so  on  till  we  arrive  at  the  99th  stratum  from  the  bottom, 
which  will,  of  course,  be  subject  to  no  more  than  one 
ounce  of  pressure. 

Springs  of  metal,  or  wood,  expand  or  contract,  until 
they  arrive  at  a  state  of  equilibrium  with  the  force  that 
is  acting  upon  them.  The  air  acts  in  the  same  way  ; 
for,  being  of  an  elastic  nature,  it  will,  of  course,  yield  to 
any  force  that  may  be  impressed  upon  it,  until  its  spring 
becomes  a  balance  to  that  force.  It  is  on  this  account 
alone  that  we  are  insensible  of  the  air's  pressure  ;  for, 
notwithstanding  the  body  of  a  man  of  ordinary  stature 
is  calculated  to  sustain  no  less  a  pressure  of  air  than 
32,400  pounds,  yet  the  spring  of  the  air  contained 
within  the  body  exactly  balances,  or  counteracts,  the 
pressure  from  without,  and  makes  him  insensible  of  the 
existence  of  any  pressure  at  all.  The  spring  and  pres- 
sure of  air  will  thus  balance  each  other  in  all  cases, 
except  when  the  communication  is  cut  off,  and  the  nat- 
ural equilibrium  is  destroyed  by  some  disturbing  cause. 


PNEUMATICS.  123 

The  air-pump  is  the  instrument  that  is  generally 
used  for  the  destruction  of  this  equilibrium  ;  for,  by 
means  of  this  machine,  the  air  may  be  taken  from  the 
interior  of  vessels  which  are  put  upon  its  plate,  and 
then  the  effects  of  the  external  and  undisturbed  air 
immediately  begin  to  show  themselves.  Thus,  for 
example,  if  a  small  glass  receiver,  which  is  open  both 
above  and  below,  be  placed  upon  the  plate  of  an  air- 
pump,  and  the  palm  of  the  hand  be  put  upon  it,  so  as  to 
cover  it  completely,  without  leaving  any  orifice  for  the 
admission  of  the  external  air,  —  as  soon  as  the  pump  is 
set  in  motion,  the  hand  will  be  forcibly  held  down  to 
the  receiver,  and  cannot  be  released  without  difficulty ; 
for  the  air  within  the  glass  being  rarefied  or  diminished 
in  quantity,  that  without  will  preponderate  by  its  weight, 
which  keeps  the  hand  down,  while  the  spring  of  that 
air  which  is  contained  in  the  hand  will  cause  its  lower 
side  to  swell,  and  enter  the  glass  to  a  considerable 
depth.  This  shows  the  necessity  of  having  all  glasses, 
to  be  used  upon  the  air-pump,  with  hemispherical  or 
rounded  tops,  that  they  may  present  a  dome,  or  arched 
form,  to  the  pressure  of  the  external  air ;  and  all  such 
glasses  are  called  by  the  general  name  of  receivers. 
If  an  open-topped  receiver  be  covered  with  a  piece  of 
flat  glass,  the  pressure  from  without  will  break  it. 

If  a  small  portion  of  the  shell  of  an  egg  be  broken 
away  at  the  small  end,  and  it  is  then  placed  under  a 
receiver,  and  the  air  is  exhausted,  the  bubble  of  air 
that  is  always  contained  in  the  large  end  will  expand, 
and  force  out  the  contents  of  the  egg.  A  withered 
apple,  placed  under  a  receiver,  will  expand,  and  appear 
fresh,  provided  its  skin  be  not  broken.  That  air  is 


124  PNEUMATICS. 

contained  in  water  appears  plain  from  the  following 
experiment :  Place  a  tumbler  of  clear  water,  in  which 
not  a  single  bubble  of  air  is  visible,  under  a  receiver, 
and  then  exhaust  it ;  the  water  will  instantly  appear  full 
of  bubbles,  which  become  large,  and  rise  to  the  top ; 
but  as  soon  as  the  air  is  returned  into  the  receiver,  they 
are  all  instantly  compressed,  and  disappear. 

The  ascent  of  water  in  a  common  pump  is  caused 
by  atmospheric  pressure  ;  for  the  water  in  the  pump 
being  raised  by  the  action  of  the  upper  pump-box,  a 
vacuum  is  created  below,  which  is  immediately  filled 
by  the  pressure  of  the  air  from  without,  which  forces 
the  water  in  the  bottom  of  the  well  upward,  to  supply 
that  vacuum.  But,  as  equal  weights  must,  of  course, 
exactly  balance  each  other,  and  as  the  weight  of  the 
atmosphere  is  limited,  it  is  evident  that  only  a  column 
of  water  of  a  certain  height  can  be  raised  by  that 
weight.  Accordingly,  it  has  been  found  that  water 
cannot  be  raised  in  a  pump,  by  the  mere  pressure  of 
the  external  air,  higher  than  32  or  33  feet ;  whence 
the  inference  is  plain,  that  a  column  of  water  of  this 
height  is  exactly  equal  in  weight  to  that  of  the  atmos- 
phere on  the  same  surface.  The  diameter  of  the 
column  of  water,  in  this  case,  is  of  no  consequence ;  be- 
cause, whatever  it  may  be,  an  equal-sized  column  of 
air  always  acts  against  it. 

This  balance  of  power  between  a  perpendicular 
column  of  water  and  atmospheric  pressure  was  first 
observed  by  Galileo,  in  erecting  a  pump  for  the  grand 
duke  of  Tuscany ;  but  he  appears  not  to  have  been 
aware  of  its  cause.  This  was  first  investigated  by 
Torricelli,  who  made  use  of  quicksilver,  a  fluid  14 


PNEUMATICS.  125 

times  heavier  than  water,  by  which  he  was  enabled  to 
produce  a  pressure  equal  to  that  of  water  with  one 
fourteenth  part  of  its  height,  and  accordingly,  his  ex- 
periments were  very  neat  and  accurate.  He  filled 
glass  tubes  of  different  sizes,  having  one  end  closed 
with  quicksilver ;  and  then,  by  covering  the  open  end, 
he  inverted  them  into  basins  filled  with  the  same 
metal.  Thus  he  found  that  the  diameters  of  the  tubes 
had  no  effect  on  the  experiments,  but  that  all  those 
which  were  less  than  28  inches  in  height,  remained 
full  of  quicksilver,  when  inverted,  and  that  in  all  those 
which  were  taller,  the  quicksilver  descended  until  it 
became  stationary  at  between  28  and  31  inches  above 
the  surface  of  that  which  was  in  the  basin.  An  empty 
space  was  thus  left  at  the  upper  end  of  the  tube,  which 
has  since  been  found  to  be  the  most  perfect  vacuum 
producible  by  art.  This  is  known  by  the  name  of  the 
Torricellian  vacuum. 

A  tube  filled  with  quicksilver,  and  thus  disposed,  is 
called  a  barometer.  In  this  instrument,  the  column, 
being  maintained  by  the  pressure  of  the  air,  must  of 
course  be  a  balance  to  that  pressure ;  and  if  the 
amount  of  pressure  changes,  as  it  is  found  to  do,  then 
the  height  of  the  mercurial  column  will  change  also. 
It  is  on  this  account  that  the  quicksilver  in  the  barom- 
eter moves  up  and  down  through  a  space  of  three 
inches,  because  the  density  of  the  air  is  never  so  great 
as  to  cause  it  to  sustain  the  quicksilver  at  more  than  31 
niches  from  the  surface  of  that  in  the  basin  below,  nor 
does  it  ever  diminish  so  as  to  allow  the  column  to 
descend  lower  than  28  inches.  The  falling  of  the 
mercury  in  the  barometer  always  indicates  that  a 
11* 


126  PNEUMATICS. 

storm  is  approaching ;  for  this  fall  takes  place  in  con- 
sequence of  the  rarefaction  of  the  air,  which  presently 
causes  the  surrounding  air  to  rush  in  to  restore  an 
equilibrium.  The  barometer  thus  becomes  a  most  in- 
valuable instrument  to  the  mariner ;  for  on  many  oc- 
casions, when  the  weather  is  perfectly  serene,  and  the 
sky  exhibits  not  the  smallest  token  of  approaching  bad 
weather,  the  mercury  is  seen  to  sink  with  uncommon 
rapidity.  The  prudent  seaman  immediately  takes  in 
sail,  and  makes  every  preparation  against  the  coming 
danger.  Scarcely  has  the  ship  been  put  into  the  con- 
dition which  the  sailors  emphatically  call  "  snug,"  when 
a  squall,  or  perhaps  a  hurricane,  bursts  from  the  sky, 
and  tears  away  the  sails,  although  furled  and  secured 
to  the  yards,  disabling  spars  and  masts,  and,  but  for  the 
timely  preparation  made  against  it,  would  have  ren- 
dered the  ship  a  complete  wreck. 

Another  useful  purpose  to  which  the  barometer  is 
made  subservient,  is  to  measure  the  height  of  moun- 
tains ;  for  as  the  mercurial  column  is  always  an  exact 
indication  of  the  pressure  produced  by  the  mass  of  air 
above  its  level,  the  mercury  must  fall  when  the  in- 
strument is  carried  from  any  lower  to  any  higher  situa- 
tion, and  the  degree  of  falling  must  always  tell  exactly 
how  much  air  has  been  left  below.  When  the  barome- 
ter, on  the  surface  of  the  earth,  stands  at  30  inches,  and 
the  temperature  is  32  Fahrenheit,  it  has  been  ascer- 
tained, by  trial,  that  taking  such  a  barometer  to  the  per- 
pendicular height  of  87  feet  lowers  the  quicksilver  just 
one  tenth  of  an  inch.  But  as  the  atmosphere  decreases 
in  density  and  weight  as  we  ascend,  something  more 
than  87  feet  must  be  ascended,  to  lower  the  mercury 


PNEUMATICS.  127 

another  tenth,  and  so  on.  By  nice  calculations  of  this 
sort,  the  system  of  measurement  has  been  brought  to 
such  perfection,  that  the  height  of  any  accessible 
mountain  may  be  ascertained  with  the  utmost  ac- 
curacy. 

That  water  is  at  all  times  contained  in  air  is  evident 
from  the  cloud  of  vapor  which  we  constantly  observe 
to  be  precipitated  whenever  a  very  clear  receiver  is  ex- 
hausted upon  the  air-pump,  and  which  is  neither  more 
nor  less  than  a  shower  of  rain  in  miniature.  The 
damp  on  our  walls  and  windows,  which  precedes  wet 
weather,  arises  from  the  same  cause ;  for  then  the  air 
is  overcharged  with  water,  and  begins  to  return  a 
part  of  it :  the  pressure  of  water  in  the  atmosphere 
Is  detected  by  the  instruments  called  hygrometers, 
which  measure  the  moisture  of  the  air.  They  are 
of  various  forms,  and  are  constructed  of  different 
materials  ;  but,  unfortunately,  most  of  them  lose  their 
action  in  course  of  time.  One  of  the  simplest  of  these 
instruments  may  be  formed  of  a  considerable  length 
of  well-twisted  flaxen  string,  suspended  from  the  ceiling 
of  a  room  about  4  inches  from  the  wall,  and  stretched 
tight  by  a  leaden  ball,  above  which  is  fixed  a  circle  of 
pasteboard  with  divisions  upon  the  edge  of  it,  and  a 
fixed  mark  on  the  wall  for  observing  their  motion. 
In  wet  weather  the  string  twists  tighter,  and  of  course 
turns  the  circle  round,  and  in  dry  weather  it  uncoils. 
There  is  a  toy  called  the  weather-house,  constructed 
on  this  principle  :  in  this,  by  the  twisting  and  untwisting 
of  the  string,  a  woman  comes  out  at  the  door  in  fine 
weather,  and  a  man  when  it  is  wet.  The  most  com- 
mon hygrometer,  which  somewhat  resembles  a  watch 


128  PNEUMATICS. 

0 

in  shape,  is  made  of  the  beard  of  a  peculiar  species 
of  wild  oat,  which  possesses  the  singular  property  of 
coiling  up  in  dry  weather,  and  unfolding  when  wet. 
A  scale-beam,  with  any  substance  capable  of  absorbing 
moisture,  such  as  a  sponge,  at  one  end,  counterpoised  by 
a  metal  weight  at  the  other,  becomes  an  hygrometer — 
since  the  sponge  will  absorb  moisture  from  the  air, 
and  become  dry  again,  by  which  it  is  made  heavier 
or  lighter  than  the  counterpoising  weight. 

Air  incorporates  not  only  with  water,  but  with  a 
great  variety  of  other  volatile  materials,  by  which  many 
of  its  characters  become  much  changed ;  and  since 
heat  assists  in  these  combinations,  so  all  warm  or  hot 
fluids  will  evaporate  more  readily  than  such  as  are 
cold.  Put  a  few  drops  of  ether  into  a  large  drinking- 
glass,  and  cover  it  with  a  plate  for  a  few  minutes, 
the  ether  will  evaporate  into  the  air,  and  will  ren- 
der it  so  inflammable  that  it  will  take  fire  on  the 
approach  of  a  taper.  Notwithstanding  the  attraction 
that  thus  appears  to  exist  between  the  air  and  various 
fluids,  yet  the  very  pressure  of  the  atmosphere  pre- 
vents their  rising  in  vapor,  or  evaporating,  upon  a  slight 
increase  of  temperature.  Thus  ether  is  the  rarest  and 
most  volatile  of  all  the  visible  fluids ;  and  when  a  cup 
containing  a  little  of  this  is  placed  under  the  receiver 
of  an  air-pump,  a  very  trifling  action  of  the  pump  will 
make  it  boil.  Water  in  the  open  air  will  not  boil  unless 
heated  to  212  degrees,  but  when  the  atmospheric  pres- 
sure is  removed,  it  boils  at  a  much  lower  temperature  ; 
and  a  glass  of  strong  ale,  when  heated  in  the  slightest 
degree  under  an  exhausted  receiver,  will  put  on  the  ap- 
pearance of  boiling.  From  these  facts  it  follows  that, 


PNEUMATICS.  129 

on  the  top  of  a  mountain,  water  will  boil  with  a  less 
degree  of  heat  than  in  a  lower  region;  and  this  has 
been  verified  by  actual  experiment 

From  the  highly  elastic  nature  of  air,  there  is  no 
limit  to  its  condensation,  which  may  be  continued  as 
long  as  there  is  strength  in  machinery  to  force  it  It 
has  been  carried  to  great  extent ;  but,  from  all  the  ex- 
periments that  have  been  tried,  it  does  not  appear  that 
condensation  produces  any  effect  on  the  fluidity,  trans- 
parency, or  other  characters,  of  air.  Various  machines 
have  been  invented  for  this  purpose.  The  air-gun  is 
the  best  example  of  the  surprising  force  which  air  is 
capable  of  exerting  when  condensed  to  a  considerable 
degree ;  for  by  means  of  this  instrument,  bullets  may  be 
propelled  with  a  force  very  nearly  equal  to  that  of 
gunpowder.  It  is  a  curious  fact,  that,  although  the 
air-pump  is  a  modern  invention,  yet  the  air-gun,  which 
is  so  nearly  allied  to  it  in  the  construction  of  its  valves 
and  condensing  syringe,  existed  long  antecedent  to  it ; 
it  was  invented  as  early  as  the  year  1408.  The  ail- 
gun  of  the  present  day,  however,  is  very  different  from 
that  of  former  times,  which  discharged  but  one  bullet 
after  a  long  and  tedious  process  of  condensation,  while 
it  now  discharges  five  or  six  without  any  visible  dimi- 
nution of  force,  and  will  even  act  upon  a  dozen,  though 
with  less  effect 

The  alternate  rarefaction  and  condensation  of  the 
atmosphere  is  the  cause  of  most  of  the  changes  of  the 
weather;  for  thus  are  produced  not  only  wind  and 
storms,  but  dew,  fog,  rain,  hail,  and  snow.  The  air, 
being  saturated  with  moisture,  lets  fall  a  part  of  it  on 
any  reduction  of  the  temperature :  the  atmosphere, 


*30  PNEUMATICS. 

which  has  been  heated  by  the  sun  during  the  day,  and 
has  received  much  moisture,  lets  it  fall  again  during 
the  night,  and  thus  causes  the  night  fogs  of  certain 
seasons,  which  float  near  the  surface  of  the  earth  until 
again  acted  upon  by  the  beams  of  the  next  morning's 
sun.  Fog,  when  condensed  by  the  combination  of  the 
minute  particles,  forms  rain ;  and  rain,  when  frozen, 
becomes  snow  or  hail. 

The  general  principles  of  aerostation,  or  navigating 
the  air  in  balloons,  are  so  little  different  from  hydro- 
statics, that  the  reader  may  be  supposed  already  to 
understand  them,  from  what  has  been  said.  It  is  a  fact 
universally  known  that,  when  a  body  is  immersed  in 
any  fluid,  if  its  weight  be  less  than  an  equal  bulk  of 
that  fluid,  it  will  rise  to  the  surface  ;  but  if  heavier,  it 
will  sink ;  and  if  equal,  it  will  remain  stationary.  For 
this  reason  smoke  ascends  into  the  atmosphere,  and 
heated  air  into  that  which  is  colder.  The  ascent  of  the 
latter  is  shown  in  a  very  easy  and  satisfactory  manner, 
by  bringing  a  red-hot  iron  under  one  of  the  scales  of  a 
balance  ;  the  balance  is  instantly  made  to  ascend  ;  for 
as  soon  as  the  iron  is  brought  under  the  scale,  the  hot 
air,  being  lighter  than  that  which  is  colder,  moves 
upward,  strikes  the  scale,  and  elevates  it.  Upon  this 
simple  principle  depends  the  whole  theory  of  aeros- 
tation ;  for  it  is  the  same  thing  whether  we  render  the 
air  lighter  by  introducing  a  quantity  of  heat  into  it,  or 
enclosing  a  quantity  of  gas,  specifically  lighter  than 
the  common  atmosphere,  in  a  certain  space  ;  both  will 
ascend,  and  for  the  same  reason.  The  power  of  hot 
air,  in  raising  weights,  may  be  shown  in  the  following 
manner.  Roll  a  sheet  of  paper  into  a  conical  form, 


PNEUMATICS.  131 

and  fasten  it,  by  its  apex,  under  the  scale  of  a  balance ; 
apply  the  flame  of  a  candle  underneath,  and  the  scale 
will  rise,  and  will  not  be  brought  into  an  equilibrium 
with  the  other,  except  by  a  much  greater  weight  than 
would  be  imagined  by  a  person  who  had  never  seen 
the  experiment. 

The  first  balloon  was  made  by  a  man  ignorant  of 
what  he  was  about  to  discover.  Seeing  the  clouds  float 
high  in  the  atmosphere,  he  thought  that,  if  he  could 
make  a  cloud  and  enclose  it  in  a  bag,  it  might  rise,  and 
carry  him  with  it  Then,  erroneously  supposing  cloud 
and  smoke  to  be  the  same,  he  made  a  fire  of  green 
wood,  and  placed  a  great  bag  over  it,  with  the  mouth 
open.  He  soon  had  the  joy  of  finding  himself  in 
the  possession  of  a  bag-full  of  smoke,  which  pres- 
ently rose  to  the  ceiling  of  the  room ;  but  he  under- 
stood not  that  the  cause  of  its  rising  was  the  hot, 
rarefied  air  within,  which,  being  lighter  than  the  sur- 
rounding air,  was  buoyed  up,  while  the  visible  part  of 
the  smoke,  which  chiefly  engaged  his  attention,  was 
really  heavier  than  the  air,  and  impeded  the  ascent  of 
the  bag.  The  hot  air  or  fire  balloon  was  afterwards 
better  understood,  and  was  used  by  aeronauts,  until  the 
more  commodious  and  less  dangerous  modification, 
called  the  inflammable  air  balloon,  or  balloon  of  hydro- 
gen gas,  was  substituted.  The  first  aeronautic  expedi- 
tions astonished  the  world,  and  endless  speculations 
were  indulged  as  to  the  important  uses  to  which  the 
new  discovery  might  be  applied  ;  but  more  mature  re- 
flection, and  recent  trials,  have  shown  that  the  balloon 
is  interesting  chiefly  as  a  philosophical  toy,  and  as 
having  furnished  the  means  of  making  some  observa- 


132  PNEUMATICS. 

tions  in  elevated  regions  of  the  atmosphere.  An  aero- 
naut may  rise  or  descend  in  the  air,  by  throwing  out 
ballast  or  letting  off  gas ;  but  he  has  no  power  of  pro- 
ducing a  lateral  motion. 

The  diving-bell  is  a  large,  heavy,  open-mouthed 
vessel,  which  is  let  down  in  the  water,  bottom  upwards, 
with  men  inside.  The  enclosed  air  keeps  out  the 
water  at  first ;  but  as  the  bell  descends,  the  pressure  of 
the  water  increasing  according  to  its  depth,  the  air  is 
compressed  within  the  bell,  and,  at  34  feet  depth,  it  is 
reduced  to  half  its  bulk.  The  bell  is  then  half  full  of 
water,  and  a  person  within  breathes  twice  as  much  air, 
at  an  inspiration,  as  he  does  at  the  surface.  When 
men  are  required  to  remain  long  under  water,  a  supply 
of  fresh  air  is  conveyed  down  by  means  of  a  forcing- 
pump,  and  the  heated  and  contaminated  air,  which  has 
served  for  respiration,  and  which  rises  to  the  top  of  the 
bell,  is  allowed  to  escape  through  an  opening.  Men 
can  work  at  a  distance  from  the  bell,  and  breathe  the 
air  from  it,  through  tubes  of  communication.  These 
operations  are  so  little  hazardous,  or  uncomfortable, 
that  the  wages  of  submarine  labor  are  very  little 
higher  than  any  other. 


OPTICS, 


Luminous  Insects. 


THIS  science  treats  of  the  phenomena  of  light  and 
vision.     Of  the  precise  character  of  light  there  are 
various  theories,  but  none  which  admit  of  actual  dern. 
xin. — 12 


134  OPTICS 

castration,  or  proof.  By  some,  it  has  been  described 
as  consisting  of  very  minute  particles,  which  are 
thrown  off  from  what  are  called  luminous  bodjes,  in  all 
directions,  and  with  immense  velocity ;  while  others 
consider  it  as  the  effect  of  an  undulation,  cr  vibration, 
produced  by  luminous  bodies  in  the  thin  and  elastic 
medium  which  is  interposed  between  them  and  the  seat 
of  our  vision ;  this  vibration  producing  an  effect  upon 
our  organs,  which  we  recognize  as  light,  analogous  to 
the  impression  of  sound  upon  the  ear,  caused  by  the 
atmosphere.  This  theory  is  called  the  undulatory 
theory  of  light ;  and  the  former  one,  in  which  light 
is  supposed  to  consist  of  material  particles,  is  called 
the  theory  of  emission.  Whatever  may  be  the  cause, 
or  absolute  nature,  of  light,  we  know  it  is  a  remarkable 
property  of  luminous  bodies  ;  that  it  enables  us  to  see 
the  luminous  objects  themselves,  as  well  as  others ; 
and  that  its  absence  produces  darkness. 

All  visible  bodies  may  be  divided  into  two  classes — 
self-luminous  and  non-luminous.  Under  the  first  head 
are  comprised  all  those  bodies  which  possess  in  them- 
selves the  property  of  exciting  the  sensation  of  light, 
or  vision ;  such  as  the  heavenly  luminaries,  terrestrial 
flames  of  all  kinds,  phosphorescent  bodies,  and  those 
substances  which  shine  by  being  heated,  or  by  friction. 
Under  the  second  class,  we  recognize  such  bodies  as 
have  not,  of  themselves,  the  power  of  throwing  off  par- 
ticles or  undulations  of  light,  but  which  possess  the 
power  of  reflecting  the  light  which  is  cast  upon  them 
by  self-luminous  bodies.  A  non-luminous  body  may 
thus,  by  reflection,  receive  light  from  another  non- 
luminous  body,  and  communicate  it  to  a  third,  and  so 


OPTICS.  135 

on ;  all  reflected  light,  however,  is  inferior,  in  point  of 
brilliancy,  to  that  which  comes  direct  from  a  self-lu 
minous  body.  The  transmission  of  light  was  formerly 
supposed  to  be  instantaneous ;  but  recent  observations 
have  shown  that,  like  sound,  it  requires  a  certain  time 
to  pass  from  one  place  to  another,  though  the  veloci- 
ty of  its  motion  is  truly  astonishing,  as  has  been  man- 
ifested in  various  ways.  Astronomers  have  proved, 
by  observing  the  eclipses  of  Jupiter's  satellites  when 
that  planet  is  nearest,  and  when  it  is  farthest,  from  the 
earth,  that  light  moves  from  the  sun  to  the  earth,  a 
distance  of  95  millions  of  miles,  in  seven  and  a  half 
minutes,  or  about  200,000  miles  during  a  single  vibra- 
tion of  a  pendulum !  So  prodigiously  great  is  this 
velocity,  that,  as  far  as  any  of  the  common  affairs  of 
life  may  be  concerned,  light  may  be  said  to  be  instanta- 
neous in  its  universal  action. 

Light  proceeds  in  a  straight  direction  from  the 
luminous  body  which  produces  it  The  direct  shining 
of  the  sun,  or  any  other  luminous  body,  is  in  the  form 
of  rays,  or  thin,  ethereal  lines,  each  acting  independ- 
ently of  the  other.  No  such  separation  of  parts,  how- 
ever, is  observable  in  common  circumstances,  in  con- 
sequence of  the  diffusive  properties  of  our  atmosphere. 
Seeing  is  simply  the  reception  of  the  direct  or  reflect- 
ed ray  from  an  object,  by  our  eye.  Until  the  rays  of 
the  sun  reach  the  spot  on  which  we  are  placed,  we 
are  neither  conscious  of  light,  nor  of  the  presence  of 
the  sun  as  an  object.  In  the  same  manner,  a  candle, 
being  lighted,  and  exposed  in  the  open  country  in  a 
dark  night,  all  who  are  able  to  see  it  are  within  the 
influence  of  its  rays ;  but  beyond  a  given  distance, 


these  rays  are  too  weak  to  produce  vision;  and  all 
who  are  in  this  remote  situation  cannot  see  the  small- 
est appearance  of  the  light.  Yet  the  number  of  rays 
which  proceed  even  from  a  common  candle  is  so  vast 
as  to  be  beyond  the  power  of  imagination  to  conceive ; 
for  if  such  a  light  is  visible  within  a  sphere  of  4  miles, 
it  follows  that,  if  the  whole  of  that  space  were  sur- 
rounded with  eyes,  each  eye  would  receive  the  im- 
pression of  a  ray  of  light.  In  proportion  as  light  ad- 
vances from  its  seat  of  production,  it  diminishes  in 
intensity.  The  ratio  of  diminution  is  agreeable  to  that 
which  governs  physical  forces ;  that  is,  the  intensity 
of  the  light  will  diminish  as  the  square  of  the  distance 
increases,  or  at  the  rate  of  1,  4,  16,  &c.  But,  in  pro- 
portion as  we  lose  in  intensity,  we  gain  in  volume  ;  the 
light  is  the  weaker  the  farther  it  is  from  the  candle,  but 
it  fills  a  wider  space. 

In  discussing  the  properties  of  light,  it  is  important 
to  consider  the  medium  through  which  it  passes,  as  air, 
water,  glass,  &c.  Any  parcel  of  rays  passing  from  a 
point,  is  called  a  pencil  of  rays ;  the  point  at  which 
converging  rays  meet,  is  called  a  focus.  Rays  may  be 
parallel,  convergent.,  or  divergent,  which  terms  will 
not  require  an  explanation.  The  point  towards  which 
they  tend,  but  which  they  are  prevented  from  reaching 
by  some  obstacle,  is  called  the  imaginary  focus. 

REFRACTION  is  the  bending  of  rays  of  light  from  the 
course  they  first  pursued.  If  the  rays,  after  passing 
through  a  medium,  enter  another  of  different  density, 
perpendicular  to  its  surface,  they  are  not  refracted,  but 
proceed  through  this  medium,  in  their  original  direc- 
tion. For  instance,  if  the  rays  of  the  sun  were  to 


OPTICS.  137 

strike  upon  the  surface  of  a  river  at  right  angles,  or 
perpendicularly  to  its  surface,  they  would  go  straight 
to  the  bottom,  and  the  line  which  they  pursued  in  the 
air  would  be  continued  in  the  water.  But  if  they  enter 
obliquely  to  the  surface  of  a  medium  either  denser  or 
more  rare  than  what  they  moved  in  before,  they  are 
made  to  change  their  direction  in  passing  through  that 
medium ;  in  other  words,  they  are  refracted.  The 
mode  of  refraction  depends  on  the  comparative  density 
or  rarity  of  the  respective  media.  If  the  medium 
which  the  rays  enter  be  denser,  they  move  through  it 
in  a  direction  nearer  to  the  perpendicular  drawn  to  its 
surface.  On  the  contrary,  when  light  passes  out  of  a 
denser  into  a  rarer  medium,  it  moves  in  a  direction 
farther  from  the  perpendicular.  This  refraction  is 
greater  or  less;  that  is,  the  rays  are  more  or  less 
bent,  or  turned  aside,  from  their  course,  as  the  second 
medium,  through  which  they  pass,  is  more  or  less 
dense  than  the  firsL  To  prove  this  in  a  satisfactory 
way,  take  an  upright  empty  vessel  into  a  darkened 
room,  which  admits  but  a  single  beam  of  light  obliquely 
through  a  hole  in  the  window-shutter.  Let  the  empty 
vessel  stand  on  the  floor  a  few  feet  in  advance  of  the 
window  which  admits  the  light,  and  let  it  be  so  ar- 
ranged that,  as  the  beam  of  light  descends  towards  the 
floor,  it  just  passes  over  the  top  of  the  side  of  the  ves- 
sel next  the  window,  and  strikes  the  bottom  on  the 
side  farthest  from  the  window.  Let  the  spot  where  it 
falls  be  marked.  Now,  on  filling  the  vessel  with  water, 
the  ray,  instead  of  striking  the  original  spot,  will  fall 
considerably  nearer  the  side  towards  the  window.  And 
12* 


138  OPTICS. 

if  we  udd  a  quantity  of  salt  to  the  vessel  of  water,  so 
as  to  form  a  dense  solution,  the  point  where  the  rays 
strike  the  bottom  will  move  still  nearer  to  the  window. 
In  like  manner,  if  we  draw  off  the  salt  water,  and 
supply  its  place  with  alcohol,  the  beam  of  light  will  be 
still  more  highly  refracted ;  and  oil  will  refract  yet 
more  highly  than  alcohol. 

The  following  simple  experiment  is  well  known: 
Take  an  empty  basin,  and  place  it  on  a  table  ;  then 
lay  a  silver  dollar  at  the  bottom  of  the  basin,  and  let 
the  spectator  withdraw  so  far  that  the  brim  of  the 
basin  hides  the  dollar.  Now,  fill  the  basin  with  water, 
and  the  dollar,  though  lying  unmoved,  will  come  com- 
pletely into  sight.  The  explanation  of  this  phenomenon 
is,  that  the  ray  of  light  producing  vision  in  the  eye 
is  bent,  as  it  emerges  from  the  water,  and  has  all  the 
effect  of  conveying  our  sight  round  a  corner.  The 
refractive  power  of  water  is  also  observable  when  we 
thrust  a  straight  stick  into  it;  we  see  that  the  stick 
seems  to  be  bent,  and  fails  in  reaching  the  point  which 
we  desired  it  should.  On  this  account,  the  aim,  by  a 
person  not  directly  over  a  fish,  must  be  made  at  a 
point  apparently  below  it,  otherwise  the  weapon  will 
miss,  by  striking  too  high.  With  regard  to  the  refrac- 
tive power  of  transparent  substances,  or  media,  the 
general  rule,  with  certain  limitations,  is  in  proportion 
to  the  densities  of  the  bodies  ;  it  increases,  for  instance, 
from  the  most  perfect  vacuum  which  can  be  formed, 
through  air,  fresh  water,  salt  water,  glass,  and  so  on. 
But  those  substances  which  contain  the  most  inflam- 
mable matter  have  the  highest  refractive  power.  It 
was  from  the  great  refractive  powers  of  the  diamond 


OPTICS.  139 

and  water,  that  Newton,  with  admirable  sagacity,  pre- 
dicted that  they  contained  inflammable  principles. 

The  refraction  of  rays  of  light  is  observable  in  the 
case  of  common  window-glass.  The  two  sides  of  a 
pane  not  being  perfectly  parallel  to  each  other,'  bodies 
seen  through  it  appear  as  if  distorted  ;  and  as  the  obli- 
quities in  the  glass  are  very  various,  the  distortions  are 
equally  grotesque  and  numerous.  Some  windows  are 
purposely  ground  on  the  surface,  to  produce  universal  and 
minute  refraction ;  and  thus  so  great  a  confusion  is  in- 
troduced among  the  rays,  that  objects  are  not  distin- 
guishable through  the  glass.  When  the  obliquities  on  the 
surface  of  one  side  of  a  piece  of  glass  stand  distinct  from 
each  other,  so  as  to  admit  of  refraction  in  a  clear  and 
distinguishable  manner,  then  each  obliquity  affords  a 
separate  view  of  an  object  on  the  opposite  side,  and 
thus  an  object  seems  to  be  multiplied  as  many  times  as 
there  are  obliquities.  The  refraction  of  light  is  also 
observable,  on  a  great  scale,  in  relation  to  our  atmos- 
phere. The  rays  of  the  sun,  on  reaching  the  confines 
of  the  atmospheric  fluid  which  envelops  the  earth,  enter  a 
medium  of  greater  density  than  that  through  which  they 
have  previously  passed,  and  consequently  are  refracted, 
or  bent.  One  obvious  effect  of  this  is,  that  we  never 
see  the  sun  in  the  actual  position  which  he  occupies. 
He  always  appears  more  or  less  raised  in  relation  to 
our  eyes,  as  was  the  case  with  the  dollar  in  the  above- 
described  experiment  of  the  basin  of  water.  This  is 
peculiarly  the  fact  in  the  morning,  when  his  earliest 
rays  meet  our  eyes.  Entering  a  denser  medium,  these 
rays  bend  round  to  meet  our  vision,  apd  we  actually 
see  the  body  of  the  sun  a  few  minutes  before  he  has 


140  OPTICS. 

risen  above  the  horizon ;  like  the  dollar  in  the  basin, 
we  see  him  round  a  corner.  In  proportion  as  the  sun 
approaches  the  zenith,  the  refraction  diminishes ;  and 
as  he  recedes  toward  setting,  it  increases.  So  con- 
siderable is  it,  in  the  hazy  atmosphere  of  evening,  that 
we  retain  a  sight  of  the  sun's  disk  after  it  has  sunk. 
The  same  phenomena  occur  in  relation  to  the  other 
heavenly  luminaries. 

From  these  explanations,  it  will  appear  that  the  di- 
rectness of  our  vision  is  at  all  times  liable  to  be  dis- 
turbed by  atmospheric  conditions.  So  long  as  the 
atmosphere  between  our  person  and  the  object  we  are 
looking  at  is  of  the  same  density,  we  may  be  said  to 
see  in  a  straight  line  to  the  object.  But  if,  by  any 
cause,  a  portion  of  that  atmosphere  is  rendered  less  or 
more  dense,  the  line  of  vision  is  bent,  or  refracted,  from 
its  course.  A  thorough  comprehension  of  this  truth  in 
science  has  banished  a  mass  of  superstition.  It  has 
been  found  that,  by  means  of  powerful  refraction,  ob- 
jects at  great  distances,  and  round  the  back  of  a  hill,  or 
considerably  beneath  the  horizon,  are  brought  into 
sight.  In  some  countries  this  phenomenon  is  called 
mirage.  The  following  is  one  of  the  most  interesting 
and  best-authenticated  cases  of  the  kind.  In  a  voyage 
performed  by  Captain  Scoresby,  in  1822,  he  was  able 
to  recognize  his  father's  ship,  when  below  the  horizon, 
from  the  inverted  image  of  it  which  appeared  in  the 
air.  "  It  was,"  says  he,  "  so  well  defined,  that  I  could 
distinguish,  by  a  telescope,  every  sail,  the  general  rig 
of  the  ship,  and  its  particular  character,  insomuch  that 
I  confidently  pronounced  it  to  be  my  father's  ship,  the 
Fame,  —  which  it  afterwards  proved  to  be,  —  though, 


OPTICS. 


141 


on  comparing  notes  with  my  father,  I  found  that  oar 
relative  position,  at  the  time,  gave  our  distance  from  one 
another  very  nearly  thirty  miles,  being  about  seventeen 
miles  beyond  the  horizon,  and  some  leagues  beyond 
the  limit  of  direct  vision ! " 


Dr.  Vince,an  English  philosopher,  was  once  looking 
through  a  telescope  at  a  ship  which  was  so  far  off,  that 


142  OPTICS. 

he  could  only  see  the  upper  part  of  the  masts.  The 
hull  was  entirely  hidden  by  the  bending  of  the  water ; 
but,  between  himself  and  the  ship,  he  saw  two  perfect 
images  of  it  in  the  air.  These  were  of  the  same  form 
and  color  as  the  real  ship ;  but  one  of  them  was 
turned  completely  upside  down. 

In  the  sandy  plains  of  Egypt,  the  mirage  is  seen  to 
great  advantage.  These  plains  are  often  interrupted 
by  small  eminences,  upon  which  the  inhabitants  have 
built  their  villages  in  order  to  escape  the  inundations 
of  the  Nile.  In  the  morning  and  evening,  objects 
are  seen  in  their  natural  form  and  position ;  but  when 
the  surface  of  the  sandy  ground  is  heated  by  the  sun, 
the  land  seems  terminated,  at  a  particular  distance, 
by  a  general  inundation ;  the  villages  which  are  be- 
yond it  appear  like  so  many  islands  in  a  great  lake  ; 
and  an  inverted  image  of  a  village  appears  between 
the  hills. 

The  Swedish  sailors  long  searched  for  a  supposed 
magic  island,  which,  from  time  to  time,  could  be  descried 
between  the  Island  of  Aland  and  the  coast  of  Upland. 
It  proved  to  be  a  rock,  the  image  of  which  was  pre- 
sented in  the  air  by  mirage.  At  one  time,  the  English 
saw  with  terror  the  coast  of  Calais  and  Boulogne,  in 
France,  rising  up  on  the  opposite  side  of  the  Channel, 
and  apparently  approaching  their  island.  But  the 
most  celebrated  example  of  mirage  is  exhibited  in  the 
Straits  of  Messina.  The  inhabitants  of  the  Calabrian 
shore  behold  images  of  palaces,  embattled  ramparts, 
houses,  and  ships,  and  all  the  varied  objects  of  towns 
and  landscapes,  in  the  air  —  being  refracted  images  from 
the  Sicilian  coast.  This  wonderful  phenomenon  is 


OPTICS.  143 

regarded  by  the  common  people  as  the  work  of  fairies, 
and  is  known  by  the  name  of  the  fata  morgana. 

COLOR  BY  REFRACTION.  One  of  the  most  remark- 
able phenomena  attending  refraction,  is,  that  the  rays 
of  light,  which  seem  to  us  to  be  white,  may  be  sep- 
arated into  rays  of  various  colors.  It  will  be  obvious 
that  light  has  the  effect  of  representing  colors  when  no 
color  substantially  exists,  by  noticing  the  glancing  and 
varied  hues  on  irregular  surfaces  of  glass,  ice,  or 
other  crystallized  substances.  The  proper  method  of 
analyzing  the  rays  of  light,  and  discovering  into  what 
colors  they  may  be  resolved,  is  by  the  use  of  ajjrwm, 
or  three-sided  rod  of  glass.  The  experiment  may  be 
made  in  the  following  manner  :  Into  a  darkened  room 
admit  a  beam  of  sunlight  through  a  hole  in  the  shut- 
ter ;  let  this  fall  upon  the  prism,  and,  instead  of  passing 
in  a  direct  line  through  it,  and  forming  a  circular  white 
spot  upon  the  wall  opposite,  the  rays  will  be  refracted 
upwards,  and  form  an  oblong  image  upon  the  wall, 
divided  into  seven  colors  —  red,  orange,  yellow,  green, 
blue,  indigo,  and  violet.  This  lengthened  image  of 
the  sun  is  called  the  solar  or  prismatic  spectrum.  No 
lines  are  seen  across  the  divisions  between  the  different 
colors,  and  it  is  extremely  difficult  for  the  sharpest  eye 
to  point  out  their  boundaries.  This  experiment  shows 
that  common  white  light  is  compounded  of  seven  dif- 
ferent colors,  and  that  they  all  differ  in  their  powers 
of  refraction  ;  that  is,  the  glass,  or  whatever  medium 
through  which  they  pass,  attracts  no  two  of  them  with  the 
same  degree  of  force.  As  they  differ  in  refraction,  so 
also  they  differ  in  their  powers  of  reflection  ;  and  hence 
arise  all  the  various  colors  of  bodies.  Those  bodies 


144  OPTICS. 

which  reflect  only  the  red  rays,  for  instance,  and  ab- 
sorb all  the  others,  appear  red  ;  and  so  of  the  other 
colors.  Those  which  reflect  all  the  rays  appear  white, 
and  those  which  absorb  all  the  rays,  or  nearly  so,  ap- 
pear black.  Hence  it  is  that  black  clothes  are  warmer 
than  any  other  color,  as  they  absorb  more  light,  and 
light  is  never  unaccompanied  by  heat.  On  the  other 
hand,  white  is  the  coolest  dress  that  can  be  worn. 

The  rainbow  is  formed  by  a  combined  process  of 
reflection  and  refraction.  It  is  never  seen,  except 
when  rain  is  falling  between  the  spectator  and  the  sky 
opposite  the  sun.  If  we  look  into  a  globe  of  glass,  or 
water,  held  above  the  head,  and  opposite  to  the  sun, 
we  shall  see  a  prismatic  spectrum  reflected  from  the 
farther  side  of  the  globe.  In  this  spectrum,  the  violet 
rays  will  be  innermost,  and  the  spectrum  vertical.  If 
we  hold  the  globe  on  a  level  with  the  eye,  so  as  to  see 
the  sun's  light  reflected  in  a  horizontal  plane,  we  shall 
see  a  horizontal  spectrum  with  the  violet  rays  inner- 
most ;  and  a  corresponding  variation  will  be  observed  in 
other  positions.  Now,  since,  in  a  shower  of  rain,  there 
will  be  drops  in  all  positions  relative  to  the  eye,  the 
eye  will  receive  spectra  inclined  at  all  angles  to  the 
horizon ;  so  that,  when  combined,  they  will  form  the 
large,  curved  spectrum  called  the  rainbow.  In  a  very 
strong  sunlight,  a  secondary  bow  is  seen  outside  of  the 
primary  one :  the  colors  are  fainter,  because  the  bow 
consists  of  rays  that  have  suffered  two  reflections  in- 
stead of  one.  Red  rainbows,  distorted  rainbows,  and 
inverted  rainbows  on  the  grass,  have  been  observed. 
The  latter  are  formed  by  the  drops  of  rain  suspended 
on  the  spiders'  webs  in  the  fields. 


OPTICS.  145 

Light  is  diffused  around  us  by  the  refractive  power 
of  the  atmosphere,  and  therefore  objects  are  quite 
visible,  though  the  rays  of  the  sun  do  not  strike 
directly  upon  them.  The  atmosphere  being  thus  a 
vehicle  of  light,  it  may  be  supposed  that,  if  we  were 
to  ascend  to  a  great  height  above  the  level  of  the  earth, 
or  beyond  the  atmosphere,  we  should  be  almost  in 
darkness,  although  we  were,  in  reality,  nearer  the 
sun.  There  is  reason  to  believe  that  such  would  be 
the  case ;  for  travellers,  who  have  ascended  to  the  sum- 
mit of  Mont  Blanc,  or  about  15,000  feet  above  the 
level  of  the  sea,  mention  that,  at  that  height,  the  sky 
appears  to  be  of  an  exceedingly  dark  blue  color,  or 
almost  black,  and  the  light  so  faint  that  the  stars  are 
visible.  We  may  understand,  from  this,  that  the  rays 
of  the  sun  travel  through  immense  regions  of  darkness 
before  .they  reach  our  atmosphere,  and  are  difiused  into 
that  universal,  soft  light  which  we  observe  around  us. 

REFLECTION  adds  to  the  brilliancy  of  the  great  mass 
of  light  transmitted  from  the  sun.  If  all  the  objects 
on  the  surface  of  our  planet  were  black,  which  is  a 
negation  of  all  color,  the  sun's  light  would  be  absorbed, 
and  we  should,  even  while  the  sun  shone,  possess  much 
less  light  than  we  now  enjoy.  But,  in  consequence  of 
the  varied  coloring  in  which  our  earth  is  dressed,  the 
sun's  rays  are  more  or  less  reflected,  and  sent  back 
into  the  general  mass  of  light  If  the  object  on  which 
the  rays  fall  be  clear,  and  polished  on  its  surface,  it 
will  possess  the  power  of  representing  the  image  of 
any  object  within  the  reach  of  its  rays.  Thus  the 
surface  of  a  smooth  lake  will  represent  the  image  of 
the  sky  above,  of  the  neighboring  hills,  or  of  any 
j  xra. — 13 


146  OPTICS. 

object  floating  on  its  surface.  But  the  phenomena  of 
reflection  are  too  familiar  to  the  reader,  to  require  any 
very  minute  description. 

A  lens  is  a  thin  piece  of  glass,  or  any  other  trans- 
parent medium,  having  one  or  both  sides  either  con- 
vex or  concave.  The  convex  surface  magnifies  ob- 
jects, and  the  concave  diminishes  them ;  for,  accord- 
ing to  the  laws  of  refraction  already  explained,  the 
rays  of  light,  falling  upon  a  convex  lens,  are  refracted 
towards  its  centre,  or  drawn  to  a  focus ;  and  as  the  eye 
judges  of  the  position  of  an  object  from  the  direction 
in  which  the  rays  last  proceed,  the  converging  rays 
will  appear  to  come  from  a  wider  extent  of  space  than 
is  real.  In  a  concave  lens,  the  rays,  being  refracted  in 
a  different  direction,  diverge,  instead  of  converging, 
and  strike  the  eye  as  if  coming  from  a  narrower  space 
than  the  reality  ;  for  this  reason,  the  apparent. size  of 
the  object  is  diminished.  Concave  mirrors  magnify, 
and  convex  mirrors  reduce  objects,  on  the  same  prin- 
ciple. The  human  eye  contains  a  natural  convex  lens, 
through  which  all  the  rays  of  light  which  cause  our 
vision  pass,  and  are  brought  to  a  focus  on  the  retina,  a 
delicate  membrane,  lining  the  back  part  of  the  eye ; 
this  is  connected  with  the  optic  nerve,  which  commu- 
nicates with  the  brain — the  organ,  or  centre,  of  all 
sensation. 


ACOUSTICS. 


THE  term  ACOUSTICS  is  derived  from  a  Greek  word 
which  signifies,  to  hear,  and  is  applied  to  that  branch  of 
natural  philosophy  which  treats  of  the  nature  of  sound, 
and  the  laws  of  its  production  and  propagation. 

Atmospheric  vibration  is  allowed  to  be  the  cause  of 
sound.  For  instance,  a  bell  is  struck  by  its  clapper ; 
the  body  of  the  bell  consequently  vibrates,  as  we  may 
assure  ourselves  by  applying  one  of  our  nails  lightly 
to  the  edge :  in  its  agitation,  it  beats,  or  makes  im- 
pulses upon  the  air,  which,  yielding  under  the  stroke, 
or  pressure,  is  compressed,  or  condensed,  to  a  certain 
distance  around.  The  compressed  air  instantly  ex- 
pands, and,  in  doing  so,  repeats  the  pressure  on  the  air 
next  in  contact  with  it,  and  thus  each  one  of  the  ori- 
ginal strokes  of  the  vibrating  metal  sends  out  a  series 
of  shells  of  compressed  air,  somewhat  like  the  waves 
dispersed  over  a  lake  from  the  dropping  of  a  stone  into 
its  placid  bosom,  and,  like  them,  always  lessening  in 
bulk  and  force.  These  shells  are  from  2  inches  to 
30  feet  in  thickness.  The  air  they  agitate  finally 
reaches  the  ear,  where  it  gives  a  similar  impulse  to  a 
very  fine  nervous  membrane,  in  the  ear,  called  the 
drum,  which  communicates  with  the  auditory  nerve, 
and  this  conveys  to  the  brain  the  sensation  of  sound. 

With  regard  to  the  velocity  with  which  the  impulse 


148  .ACOUSTICS. 

of  sound  advances,  it  appears,  from  the  most  accurate 
experiments,  on  the  discharge  of  pieces  of  ordnrnc^, 
and  marking  the  interval  between  the  flash  and  the 
report,  at  a  distance  carefully  measured,  that,  when  the 
atmosphere  is  at  the  temperature  indicated  by  62°  of 
Fahrenheit,  sound  travels  at  the  rate  of  1125  feet  per 
second,  which  is  nearly  equal  to  the  velocity  of  a  can- 
non-ball, the  moment  it  issues  from  the  piece.  The 
ball  is  very  speedily  retarded  by  the  resistance  of  the 
air,  but  the  sound  advances  with  undiminished  velocity, 
though  unequal  intensity.  It  will  travel  a  mile  in  little 
more  than  four  seconds  and  a  half,  or  twelve  miles  and 
three  fourths  a  minute. 

On  this  depends  an  easy  method  of  determining,  in 
many  cases,  our  distance  from  objects,  and  which  may 
often  prove  useful,  particularly  in  thunder-storms.  We 
have  only  to  observe,  in  seconds,  the  interval  between 
the  flash  and  the  report,  and  allow  four  seconds  and  a 
half  to  every  mile,  or  1125  feet  to  every  second.  It  is 
remarkable,  also,  that  all  kinds  of  sounds,  strong  or 
weak,  acute  or  grave,  advance  with  the  same  velocity  ; 
and  this  arises  from  the  circumstance,  that  all  the  oscil- 
latory movements  in  the  air,  however  minute  or  ex- 
tended, are  performed  each  in  the  very  same  interval 
of  time.  For  every  degree  of  Fahrenheit  above  62°, 
tne  velocity  of  sound  is  increased  one  foot  and  about  a 
seventh  ;  and  for  every  degree  below  62°,  it  is  les- 
sened in  the  same  measure ;  so  that,  when  the  tem- 
perature is  at  the  freezing  point,  the  rate  is  only  1090 
feet  per  second. 

That  water  is  a  vehicle  of  sound,  as  well  as  the  air, 
is  proved  by  various  circumstances,  particularly  by  the 


ACOUSTICS.  149 

fact,  that  a  bell  rung  under  the  water  can  be  heard 
above ;  and  if  the  head  of  the  auditor  be  also  under 
water,  it  will  be  still  more  distinctly  heard.  The 
sound  which  the  sonorous  body  produces,  however,  is 
graver  than  that  which  it  gives  forth  in  the  air.  That 
the  atmosphere  is  necessary  for  the  transmission  of 
sound  is  evident  from  the  fact,  that  a  bell  rung  in  the 
exhausted  receiver  of  an  air-pump  can  scarcely  be 
heard.  Smooth  bodies  form  favorable  channels  of 
sound ;  as,  for  example,  the  surface  of  ice,  snow,  water, 
or  the  hard  ground.  Savages,  it  is  well  known,  are  in 
the  habit  of  putting  their  ear  to  the  ground  in  order  to 
discover  the  approach  of  enemies,  or  beasts  of  prey. 

Tubes  convey  sounds  with  great  accuracy,  and  to 
great  distances ;  and  this  property  has  been  applied  to 
various  useful  objects.  The  most  valuable  of  these 
purposes  is  that  of  examining  the  chests  of  persons 
supposed  to  possess  pulmonary  affections.  This  is 
done  by  means  of  the  stethoscope,  an  instrument  which 
resembles  a  small  trumpet.  The  wide  end  of  the  in- 
strument is  applied  to  the  body,  and  the  other  is  held 
to  the  ear  by  the  physician,  who  then  has  a  very  clear 
perception  of  the  sounds  caused  by  the  action  of  the 
lungs,  and  can  judge  whether  they  be  healthy  or  the 
reverse.  A  person  of  skill  can  exactly  describe  the 
condition  of  the  lungs,  from  the  nature  of  the  sounds 
that  thus  reach  his  ear. 

In  a  public  exhibition  in  London,  there  has  long  been 
shown  an  apparatus,  consisting  of  a  four-footed  stand, 
and  several  trumpet-mouthed  tubes,  from  any  one  of 
which  a  spectator  will  receive  a  ready  answer  to  a 
question.  The  answer  is  said  to  come  from  the  "  in- 
13* 


150  ACOUSTICS. 

visible  girl ; "  and  the  true  explanation  of  the  puzzle  is, 
that  a  secret  tube,  in  the  legs  of  the  apparatus,  commu- 
nicates the  sounds  to  a  girl  in  a  neighboring  apartment. 
Sound  requires  a  certain  length  of  time  to  travel  from 
one  place  to  another. 

It  is  on  account  of  this  principle  that,  in  long  ranks 
of  soldiers,  where  two  bands  of  music  are  placed 
at  a  considerable  interval  from  each  other,  it  is  impos- 
sible for  the  two  bands  to  keep  time.  They  may, 
indeed,  play  together,  but  each  soldier  will  hear  the 
nearest  sounds  quickest,  and  thus  they  will  seem  to 
be  out  of  time.  It  is  often  noticed,  too,  that  if,  from 
an  eminence,  we  look  upon  a  long  column,  which  is 
marching  to  a  band  of  music  in  front,  the  various 
ranks  do  not  step  exactly  together.  Those  in  the  rear 
are,  in  each  step,  a  little  later  than  those  before  them. 
This  produces  a  sort  of  undulation  in  the  whole  column, 
which  is  difficult  to  describe,  but  which  all  who  have 
noticed  it  will  understand.  Each  rank  steps,  not  when 
the  sound  is  made,  but  when,  in  its  progress  down  the 
column,  at  the  rate  of  1125  feet  per  second,  it  reaches 
their  ears.  Those  who  are  near  the  music  hear  it  as 
soon  as  it  is  produced,  while  the  others  must  wait  till 
sufficient  time  shall  have  elapsed  for  it  to  have  passed 
through  the  air  to  them. 

Should  a  commander  stand  at  a  distance  of  a  fifth 
of  a  mile  from  his  army,  and  command  them  to  fire, 
they  might  all  obey  at  the  moment  when  the  word  of 
command  reached  them  ;  but  the  officer  will  hear  the 
report  of  the  guns  from  those  at  the  side  nearest  him 
first,  then  those  a  little  farther  off,  and  so  on  to  the 
most  remote.  Thus,  though  all  might  obey  with  equal 


ACOUSTICS.  151 

alacrity,  the  sounds  will  not,  and  cannot,  appear  simul- 
taneous, for  the  report  of  the  distant  guns  must  be 
delayed  long  enough  for  the  command  to  pass  from  the 
officer  to  the  men,  and  then  for  the  sound  to  return. 
All  attempts,  therefore,  to  make  the  firing  appear 
exactly  simultaneous  from  a  long  line,  must  be  in  vain. 
An  echo,  or  duplication,  of  sound,  is  one  of  the  most 
interesting  phenomena  in  acoustics.  The  cause  of  it 
is  precisely  analogous  to  the  reaction  of  a  wave  of 
water.  When  a  wave  of  water  strikes  the  precipitous 
bank  of  a  river,  it  is  thrown  back  in  a  diagonal  direc- 
tion to  the  side  whence  it  came,  and  then  again  strikes 
on  the  bank.  In  the  same  manner,  the  pulses,  or 
waves,  of  sound  are  reflected,  or  thrown  back,  from  flat 
surfaces  which  interrupt  them,  and,  thus  returning,  pro- 
duce what  we  call  an  echo.  It  is  evident  that  the 
smoother  the  surface  which  reflects  the  sound,  the 
more  perfect  will  be  the  reverberation.  An  irregular 
surface,  by  throwing  back  the  wave  of  sound  at  irreg- 
ular intervals,  will  so  confound  and  distract  it,  that  no 
distinct  or  audible  echo  will  be  reflected.  On  the  con- 
trary, a  regular  concave  surface  will  be  concentrated 
into  a  focus  capable  of  producing  a  very  powerful 
effect.  The  velocity  with  which  an  echo  returns  to 
the  spot  where  the  sound  originates,  depends,  of  course, 
upon  the  distance  of  the  reflecting  surface ;  and  since 
sound  travels  at  the  rate  of  1 125  feet  in  a  second,  a 
rock  situated  at  half  that  distance  will  return  an  echo 
in  exactly  one  second.  The  number  of  syllables 
which  we  pronounce  in  a  second  will,  in  such  a  time, 
be  repeated  distinctly,  while  the  end  of  a  long  sentence 
would  blend  with  the  commencement  of  the  echo. 


152  ACOUSTICS. 

An  echo  may  be  double,  treble,  or  even  quadruple 
according  to  the  nature  and  number  of  the  projecting 
surfaces  from  and  to  which  the  sound  is  allowed  to 
play.  Distinctly-marked  echoes  of  this  combined  and 
planned  order  may  sometimes  be  heard  in  the  vaults  of 
cathedrals  —  in  which  case,  the  waves  of  sound  are 
driven  from  side  to  side  of  a  deeply-groined  arch,  and 
reverberate  in  protracted  peals.  One  of  the  most  inter- 
esting echoes  of  this  kind  in  nature  is  that  which  occurs 
on  the  banks  of  the  Rhine,  at  Luxley.  If  the  weather 
be  favorable,  the  report  of  a  musket  fired  on  one  side 
is  repeated  from  crag  to  crag,  on  opposite  sides  of  the 
river  alternately. 

There  are  some  remarkable  echoes  in  churches, 
arising  from  peculiarities  in  the  construction.  In 
erecting  the  baptistry  of  the  church  of  Pisa,  the  archi- 
tect disposed  the  concavity  of  the  cupola  in  such  a 
manner,  that  any  noise  from  below  is  followed  with  a 
very  loud  and  long  double  echo.  Two  persons  whis- 
pering, and  standing  opposite  to  each  other,  with  their 
faces  near  the  wall,  can  converse  together  without 
being  overheard  by  the  company  between.  This 
arises  from  the  elliptical  form  of  the  cupola,  each  per- 
son being  placed  in  the  focus  of  the  ellipsis.  In  the  ca- 
thedral church  of  Gloucester,  England,  there  is,  or  was, 
a  whispering  gallery  about  the  eastern  extremity  of  the 
choir,  which  extends  from  one  end  of  the  church  to  the 
other.  If  two  persons  placed  at  distant  points  speak 
to  one  another  in  the  lowest  voice,  it  is  distinctly  heard. 
A  similar  effect  is  produced  in  the  vestibule  of  the  ob- 
servatory of  Paris,  and  in  the  cupola  of  St.  Paul's, 
London.  A  tourist  has  mentioned  that  in  Italy,  on  the 


ACOUSTICS.  153 

way  to  Naples,  and  two  days'  journey  from  Rome,  he 
saw  in  an  inn  3  square  vault,  where  a  whisper  could 
easily  be  heard  at  an  opposite  corner,  but  not  at  all  on 
the  side  corner  that  was  near  to  you.  This  property 
was  common  to  each  corner  of  the  room.  He  saw 
another,  on  the  way  from  Paris  to  Lyons,  in  the  porch 
of  a  common  inn,  which  had  a'  round  vault.  When 
any  person  held  his  mouth  to  the  side  of  the  wall,  sev- 
eral persons  could  hear  his  whisper  on  the  opposite  side. 

The  whispering  gallery  in  St.  Paul's,  London,  is  a 
great  curiosity.  It  is  140  yards,  in  circumference,  and 
is  just  below  the  dome,  which  is  430  feet  in  circumfer- 
ence. A  stone  seat  runs  round  the  gallery  along  the 
front  of  the  wall.  On  the  side  directly  opposite  the 
door  by  which  visitors  enter,  several  yards  of  the  seat 
are  covered  with  matting,  on  which  the  visitor  being 
seated,  the  man  who  shows  the  gallery  whispers,  with- 
the  mouth  near  the  wall,  at  the  distance  of  140 
feet  from  the  visitor,  who  hears  his  words  in  a  loud 
voice,  seemingly  at  his  ear.  The  mere  shutting  of  the 
door  produces  a  sound  like  a  peal  of  thunder  rolling 
among  the  mountains.  The  effect  is  not  so  perfect  if 
the  visitor  sits  down  half  way  between  the  door  and  the 
matted  seat,  and  much  less  if  he  stands  near  the  man 
who  speaks,  but  on  the  other  side  of  the  door. 

It  is  of  great  importance  that  buildings  designed  for 
large  auditories  should  be  constructed  in  such  a  man- 
ner that  the  voice  of  the  speaker  will  neither  echo  from 
the  walls,  nor  be  lost  to  the  hearers.  The  best-known 
form  of  apartment,  for  the  proper  distribution  of  sound, 
is  that  in  which  the  length  is  from  a  third  to  a  half 
more  than  the  breadth ;  the  height  somewhat  greater 


154  ACOUSTICS. 

than  the  breadth,  and  having  a  roof  bevelled  off  all 
round  the  sides.  This  species  of  ceiling,  technically 
called  a  coved  or  coach  roof,  from  its  being  lower  at 
the  sides  than  at  the  centre,  is,  in  all  cases,  best  suited 
for  conveying  sounds  clearly  to  the  ears  of  auditors. 
MUSICAL  SOUNDS.  Thei'e  is  a  peculiar  character  in 
sounds,  depending  on  "the  nature  of  the  sounding  body. 
A  blow  with  a  hammer,  or  the  report  of  a  pistol,  pro- 
duces only  a  noise.  But  if  a  body  be  of  such  a  thin- 
ness and  tightness  as  to  produce  a  succession  of  im- 
pulses of  a  sufficient  degree  of  quickness,  a  tone  is  the 
result — namely,  a  sound  composed  of  a  great  number 
of  noises,  all  so  close  upon  each  other  that  they  bring 
but  one  result  to  the  ear.  Wires  and  strings  of  metal 
and  catgut,  slips  of  metal,  fine  membranes,  and  columns 
of  the  air  itself,  enclosed  in  tubes,  are  the  most  familiar 
•means  of  producing  sounds  of  this  kind.  Such  sounds 
are  said  to  be  musical. 

The  study  of  musical  sounds,  as  a  branch  of  natural 
philosophy,  is  calculated  perhaps  to  give  as  much  pleas- 
ure to  the  man  of  science  as  music  itself  can  convey 
to  those  who  are  gifted  with  what  are  called  good  ears. 
The  natural  character  of  these  sounds,  and  their  rela- 
tions to  each  other,  are  very  remarkable  ;  while  the 
relation  of  the  whole  to  the  human  mind  must  be 
regarded  as  one  of  the  most  interesting  proofs  of  cre- 
ative design  which  the  entire  circle  of  nature  presents. 
The  principal  sounds  in  music  may  be  said  to  be 
only  seven  in  number.  There  are  other  five,  which 
may  be  produced  by  the  voice  with  some  difficulty ; 
but  the  voice  in  an  untutored  condition  gives  forth  only 
seven.  The  notes  are  of  different  degrees  of  shrill- 


ACOUSTICS.  155 

one  rising  above  another,  in  succession.  A  per- 
son who  knows  nothing  of  music  beyond  having  heard 
another  sing  or  play,  and  having  seen  the  key-board 
of  a  piano-forte,  will  be  ready  to  say  that  there  are 
more  notes  than  seven  ;  but  there  are  only  seven  that 
are,  strictly  speaking,  various.  The  voice,  or  an  instru- 
ment, may  run  up  into  other  notes ;  but  all  of  these  are 
repetitions  of  the  first  seven,  and  identical  respectively 
with  them,  in  all  regards  except  shrillness.  In  ordi- 
nary piano-fortes,  there  are  at  least  six  repetitions  of 
the  seven  notes,  so  that  the  uppermost  keys  are  more 
piping  than  the  voice  of  a  child,  while  the  lowest  rum- 
ble like  a  drum. 

The  seven  notes  are  named  Do,  Re,  Mi,  Fa,  Sol, 
La,  Si,  or  by  the  first  seven  letters  of  the  alphabet,  in 
a  peculiar  arrangement,  namely,  C,  D,  E,  F,  G,  A,  B. 

There  are  many  curious  facts  connected  with  the 
harmonious  notes.  The  cries  of  a  city — that  is,  the 
scarcely  articulate,  but  often  very  musical  sounds 
uttered  by  persons  selling  things  in  the  streets — gen- 
erally rise  on  thirds  or  fifths,  sometimes  on  octaves ; 
and  this,  although  few  of  these  poor  people  have  ever 
been  taught  music.  The  cry  of  oysters  by  women  in 
Edinburgh  is  always  on  an  octave.  Teachers  of  elo- 
cution are  always  aware  that  human  beings,  in  general, 
make  such  transitions  of  voice  naturally,  under  the  in- 
fluence of  certain  feelings.  For  example,  a  person 
indifferently  surprised  at  hearing  a  friend  say,  "  I  was 
the  person  who  did  so  and  so,"  will  say, "  Was  it  you  ?  " 
rising  only  a  third  at  the  last  word.  If  greatly  sur- 
prised, the  rise  will  be  a  fifth.  There  may  even  be  so 
great  a  degree  of  astonishment,  that  the  word  "  you  " 


156  ACOUSTICS. 

may  begin  on  one  note  and  terminate  on  its  octave. 
The  answer,  "  Yes,  it  was  I ! "  will  show  corresponding 
declension^  or  falls  of  voice.  We  thus  see  how  truly 
music  is  a  species  of  natural  language.  Unquestion- 
ably, every  shade  of  human  feeling  can  be  represented 
by  successions  of  its  sounds,  apart  altogether  from  its 
words. 

With  respect  to  the  sounds  produced  by  wind  in- 
struments, the  effect  is  caused  by  the  vibration  of  a 
column  of  air  confined  at  one  end,  and  either  open  or 
shut  at  the  other.  The  length  of  the  sounding  column 
determines  the  nature  of  the  vibrations ;  but  along 
with  the  fundamental  tone,  there  are  interior  and  sub- 
ordinate vibrations.  The  whole  column  divides  itself 
into  regular  portions,  equal  to  the  half,  the  third,  and 
so  on,  of  the  longitudinal  extent,  in  the  same  man- 
ner as  is  the  case  in  stringed  instruments.  We  may 
observe  something  similar  to  these  vibrations  in  the 
contraction  and  expansion  of  a  long  and  very  elastic 
string,  to  one  extremity  of  which  a  ball  is  attached. 
A  spiral  spring  also  shows,  and  perhaps  more  clearly, 
the  repeated  stretching  and  recoil.  If  suddenly  struck 
at  one  end,  it  will  exhibit  not  only  a  vibration  through- 
out its  whole  extent,  but  likewise  partial  ones,  which 
wind,  like  a  snake,  along  the  chain  of  elastic  rings.  If 
the  air  be  struck  with  great  force,  the  subordinate  vi- 
brations sometimes  predominate,  and  yield  the  clearest 
and  loudest  tones.  This  may  be  observed  in  the  dying 
sounds  of  a  bell,  which  rise  one  or  two  octaves,  and 
expire  in  the  acutest  note.  Upon  the  degree  of  force 
with  which  the  instrument  is  blown,  depends  the  per- 
formance of  the  bugle-horn,  whose  compass  is  very 


ACOUSTICS.  157 

small,  consisting  only  of  the  simplest  notes.  In  other 
wind  instruments,  the  nature  of  several  notes  produced 
depends  upon  the  length  and  size  of  the  tube,  or  the 
positions  of  the  holes  in  its  sides. 

In  the  organ  there  is  a  pipe  for  each  note,  and  wind 
is  admitted  from  the  bellows  to  the  pipes  by  the  action 
of  keys  similar  to  those  of  a  piano-forte.  The  organ 
may  be  played,  also,  by  a  barrel,  made  to  turn  slowly 
under  the  keys,  and  to  lift  them,  in  passing,  by  means 
of  pins  projecting,  at  certain  determinable  intervals, 
from  the  surface  of  the  barrel.  In  wind  instruments 
which  are  furnished  with  reeds,  the  tone  depends  on 
the  stiffness,  weight,  length,  &c.,  of  the  vibrating  plate, 
or  tongue,  of  the  reed,  as  well  as  on  the  dimensions  of 
the  tube,  or  space,  with  which  it  is  connected. 


xm.— 14 


ELECTRICITY. 


ELECTRICITY,  from  the  Greek  word  electron,  amber, 
properly  signifies  the  science  which  treats  of  the  phe- 
nomena of  attraction  and  repulsion  produced  by  the 
friction  of  amber,  in  which  substance  these  phenomena 
were  first  observed.  As  similar  appearances,  however, 
were  afterwards  observed  in  sealing-wax,  glass,  and  a 
vast  number  of  other  bodies,  the  term  has  been  ex- 
tended so  as  to  embrace  the  operation  of  this  principle 
wherever  it  is  found.  The  property  exhibited  by 
amber  in  attracting  light  bodies  was  known  more  than 
600  years  before  Christ ;  and  Thales  of  Miletus,  in  en- 
deavoring to  account  for  it,  ascribed  to  this  substance 
the  functions  of  an  animated  being.  Singularly  enough, 
although  this  property  was  known  to  both  ancients  and 
moderns,  no  experiments  seem  to  have  been  made  upon 
the  subject  before  the  17th  century,  when  Dr.  Gilbert 
discovered  that  the  electrical  attraction  resided,  not 
only  in  amber,  but  in  the  diamond  and  many  other 
stones,  glass,  sulphur,  sealing-wax,  resin,  alum,  &c. 
After  this,  experiments  and  researches  were  made  by 
many  eminent  men,  among  whom  were  Sir  Isaac 
Newton  and  Dr.  Franklin  ;  and  the  electric  phenomena, 
connected  as  they  are  now  known  to  be  by  certain 
well-ascertained  laws,  form  together  the  most  complete 
and  important  addition  to  the  physical  sciences  which 
has  been  made  since  the  time  of  Newton. 


ELECTRICITY.  159 

The  simplest  and  most  usual  mode  of  producing 
electricity  is  by  friction.  If  we  rub  a  piece  of  amber 
with  dry  fur  or  woollen  cloth,  and  then  hold  the  amber 
over  any  light  substance,  as  small  pieces  of  paper,  or 
the  down  of  a  feather,  the  light  body  will  be  attracted 
by  the  amber.  The  same  effect  will  be  produced  by 
rubbing  the  crystal  of  a  watch  upon  the  sleeve  of  the 
coat,  and  still  more  powerfully  by  rubbing  a  glass  tube 
with  a  piece  of  dry  silk.  In  this  latter  case,  when  the 
tube  is  rubbed  in  the  dark,  sparks  of  brilliant  light,  ac- 
companied with  a  crackling  sound,  will  be  emitted  as 
long  as  the  friction  is  continued.  In  like  manner,  if  a 
dry  black  silk  ribbon,  about  two  feet  long,  be  laid  upon 
a  white  one  of  the  same  length,  and  be  drawn  over 
woollen  cloth,  or  silk  velvet,  or  even  between  the  finger 
and  thumb,  they  will  be  found  to  adhere  strongly 
to  each  other.  In  a  dark  room,  the  separation  of  the 
ribbons  will  be  accompanied  with  a  flash  of  light,  and 
either  of  the  ribbons,  when  separated  from  the  other, 
will  attract  light  substances. 

Now,  in  these  three  simple  experiments,  the  amber, 
the  glass,  and  the  silk  ribbons,  have  obviously  received 
new  properties,  which  they  did  not  possess  before  they 
were  rubbed  —  namely,  the  property  of  attracting  light 
bodies,  and  the  property  of  emitting  light  in  the  dark. 
These  properties  are  called  electrical.  The  amber, 
the  glass,  and  the  ribbons,  are  said  to  be  excited  by 
friction.  The  power  of  drawing  to  themselves  light 
bodies  is  called  electrical  attraction,  to  distinguish  it 
from  the  attraction  of  cohesion,  of  gravity,  and  of 
magnetism.  The  light  emitted  in  the  dark  is  named 
the  electric  spark,  and  the  body  which  is  capable  of 


160  ELECTRICITY. 

acquiring  these  properties  is  called  an  electric.  By 
rubbing  a  great  number  of  other  bodies  with  woollen 
cloth,  fur,  silk,  &c.,  they  are  found  to  exhibit  the  same 
properties  as  amber  and  glass ;  while  another  class  of 
bodies  exhibits  no  such  properties.  Hence  bodies  are 
divided  into  two  great  classes — namely,  electrics  and 
non-electrics.  The  following  is  a  list  of  electrics  ar- 
ranged in  the  order  of  their  perfection  :  glass,  the 
precious  stones,  amber,  sulphur,  shell-lac,  and  all  resin- 
ous bodies  ;  bituminous  substances  ;  silk,  wax,  cotton, 
dry  paper ;  dry  animal  substances,  as  feathers,  wool, 
hair,  parchment,  and  leather ;  dry  sugar,  ice  of  dis- 
tilled water,  oils,  metallic  oxides,  ashes,  dry  vegetable 
substances,  and  hard  stones. 

The  electrical  machine  consists  of  a  cylinder,  or  cir- 
cular plate  of  glass,  mounted  in  a  frame,  so  that  it  can 
be  turned  rapidly  round  on  its  axis  by  means  of  a 
handle.  On  one  side  of  it  is  placed  a  small  cushion 
covered  with  silk,  against  which  the  glass  is  rubbed 
during  its  rotatory  motion  ;  and  on  the  other  side,  a  brass 
or  metal  tube,  resting  upon  a  stand  of  glass,  for  the 
purpose  of  collecting  the  electricity  generated  during 
the  excitation  of  the  cylinder  or  plate.  When  this  is 
turned  briskly  round,  the  motion  will  be  accompanied 
by  a  crackling  noise  ;  and  if  in  the  dark,  streams  of 
bluish  light  will  be  perceived  directed  toward  the  sharp 
points  with  which  the  metal  tube  is  furnished  for  the 
purpose  of  drawing  off  the  electricity  from  the  glass. 
This  tube  may  thus  be  highly  charged  with  elec- 
tricity, and  when  removed  from  the  machine,  will 
retain  its  electrical  properties,  and  will,  by  simple  con- 
tact, communicate  a  portion  of  its  electricity  to  another 


ELECTUICITT.  161 

isolated  conducting  substance,  or  be  discharged  by 
touching  one  not  isolated.  If,  with  a  moderate  charge, 
it  be  touched  with  the  finger,  a  sensation  like  the 
pricking  of  a  needle  is  felt,  accompanied  with  a  feint 
spark  apparently  penetrating  the  finger. 

Bodies  are  either  conductors  or  non-conductors  of 
electricity.  The  best  conductors  are  metals  and  water ; 
the  best  non-conductors  are  glass,  wax,  gum,  resin,  &c. 
The  quantity  of  electricity  which  can  be  communicated 
to  a  perfect  conductor  is  very  great,  but  it  appears  to 
have  its  limit  If,  from  different  sources  of  electricity, 
we  charge  a  metallic  ball,  and  so  continue  to  charge,  we 
shall  presently  find  that  the  ball  will  discharge  itself 
through  the  air  into  the  nearest  conducting  body,  when 
a  spark,  describing  apparently  a  zigzag  course,  will  be 
observed.  This  spark  travels  with  immense  velocity, 
and  is  accompanied  by  a  very  audible  sound.  If 
received  by  the  body  of  a  man  or  animal,  it  produces 
through  a  part  or  whole  of  the  system  an  instant 
muscular  contraction,  which  may  be  rendered 
ciently  strong  to  cause  death,  but  in  more  moderation 
has  been  used  to  advantage  in  some  diseases. 

Electricity  had  long  been  an  object  of  study  with 
men  of  science,  yet  little  was  done  towards  elucidating 
the  theory  of  it,  when  a  discovery  was  unexpectedly 
made  which  raised  the  science  to  an  extraordinary 
degree  of  estimation.  This  discovery  consisted  in  the 
art  of  accumulating  electricity  by  means  of  the  Leydem, 
jar.  In  the  year  1745,  Von  Heist,  a  German,  made  an 
experiment  of  which  he  gives  the  following  curious 
account :  "  When  a  nail,  or  piece  of  thick  brass  wire, 
is  put  into  a  small  apothecary's  phial,  and  electrified, 
K  14* 


162  ELECTRICITY. 

remarkable  effects  follow  ;  but  the  phial  must  be  very 
dry  or  warm.  I  commonly  rub  it  over  beforehand  with 
a  finger,  on  which  I  put  some  pounded  chalk.  If  a  little 
mercury,  or  a  few  drops  of  spirit  of  wine,  be  put  into 
it,  the  experiment  succeeds  the  better.  As  soon  as 
this  phial  and  nail  are  removed  from  the  electrifying 
glass,  or  the  prime  conductor  to  which  it  has  been  ex- 
posed is  taken  away,  it  throws  out  a  pencil  of  flame  so 
long,  that,  with  this  burning  machine  in  my  hand,  I 
have  taken  above  sixty  steps  in  walking  about  my 
room.  When  it  is  electrified  strongly,  I  can  take  it 
into  another  room,  and  fire  spirit  of  wine  with  it.  If, 
while  it  is  electrifying,  I  put  my  finger,  or  a  piece  of 
gold  which  I  hold  in  my  hand,  to  the  nail,  I  receive  a 
shock  which  stuns  my  arms  and  shoulders.  A  tin 
tube,  or  a  man,  placed  upon  electrics,  is  electrified 
much  stronger  by  this  means  than  in  the  common 
way.  When  I  present  this  phial  and  nail  to  a  tin 
tube  fifteen  feet  long,  nothing  but  experience  can 
make  a  person  believe  how  strongly  it  is  electrified." 

In  the  above  experiment,  as  the  phial  was  of  small 
dimensions,  and  as  the  circumstances  essential  to  its 
greatest  effects  were  not  combined,  because  they  were 
unknown,  the  power  of  the  electricity  accumulated  was 
inconsiderable  :  but  soon  afterwards  the  art  of  giving  a 
strong  shock  was  discovered  in  Holland,  because  the 
vessels  employed  happened  to  be  larger.  As  it  was 
known  that  the  air,  or  the  particles  floating  in  it,  ab- 
stracted the  power  of  electrified  bodies,  so  that  even 
insulation  was  no  remedy  against  their  being  in  a  short 
time  deprived  of  it,  the  idea  occurred  to  Muschenbroek 
and  some  of  his  friends,  that,  if  the  electrified  body 


ELECTRICITY.  163 

were  entirely  surrounded  by  a  non-conductor,  the  dis- 
sipation of  the  electricity  would  in  a  great  measure  be 
prevented.  To  ascertain  this,  a  quantity  of  water  was 
put  into  a  bottle,  and  electrified  till  it  was  thought  to  be 
fully  charged ;  but  here  the  original  design  of  the  ex- 
periment was  lost  sight  of  by  an  unexpected  result, 
which  absorbed  all  their  attention.  One  of  the  per- 
formers, happening  to  hold  his  vessel  in  one  hand,  while 
he  endeavored  to  disengage  it  from  the  conductor  with 
the  other,  suddenly  received  a  shock  which  stunned 
and  terrified  him  in  a  high  degree.  In  this  manner 
was  discovered  what  still  continues  to  be  called  the 
electric  shock.  At  this  day,  it  excites  a  smile  to  ob- 
serve the  terms  in  which  the  shock  is  spoken  of  by 
several  of  those  who  first  submitted  to  its  effects. 
Muschenbroek,  who  tried  the  experiment  with  a  thin 
glass  bowl,  told  his  friend  Reaumur,  that  he  felt  him- 
self struck  in  his  arms,  shoulders,  and  breast ;  that  he 
lost  his  breath  for  a  time,  and  did  not  feel  himself  well 
again  for  two  days.  He  adds,  that  he  would  not  take 
a  second  shock  for  the  whole  kingdom  of  France. 
In  terms  almost  equally  heightened  by  terror,  speaks 
Allemand.  Though  he  made  the  experiment  with  only 
a  common  beer-glass,  he  declares  that  he  lost  his  breath 
for  some  moments,  and  felt  such  an  intense  pain  in  his 
nght  arm,  that  he  was  alarmed  for  the  consequences. 
Other  philosophers,  however,  were  found,  who  had  the 
resolution  to  take  shocks  of  great  intensity ;  and  one 
of  the  most  hardy  wished  that  he  might  die  by  the 
electric  shock,  that  his  death  might  furnish  an  article 
for  the  Memoirs  of  the  Parisian  Academy ! 

After  the  art  of  giving  a  shock  by  means  of  a  phial 


164  ELECTRICITY. 

or  jar  had  been  discovered,  the  art  of  combining  sev- 
eral jars,  so  as  to  unite  their  powers  in  one  discharge, 
soon  followed,  and  this  improvement  constituted  what  is 
now  called  a  'battery.  It  was  made  by  Dr.  Franklin, 
and  resulted  from  his  reflections  on  the  phenomenon  of 
the  Leyden  jar.  It  had  been  found  that,  by  coating  the 
outside  of  the  jar  with  a  conducting  substance,  which 
communicated  by  a  wire  with  the  person  who  dis- 
charged it,  the  strength  of  the  shock  was  exceedingly 
increased  ;  and  that,  unless  some  conducting  substance 
was  in  contact  with  the  outside  of  the  jar,  no  charge 
could  be  given.  Franklin,  in  accounting  for  this  cir- 
cumstance, suggested  that  a  charged  phial  or  jar  con- 
tained no  more  electricity  than  before ;  that  as  much 
was  lost  on  one  side  as  was  gained  by  the  other ;  and 
that,  to  discharge  it,  nothing  more  was  necessary  than  to 
make  a  communication  between  the  two  sides  :  the  elec- 
tricity being  by  this  means  enabled  to  regain  its  equi- 
librium, that  equilibrium  was  instantly  restored,  and  no 
signs  of  electricity  remained.  He  also  demonstrated 
by  experiments  that  the  electricity  did  not  reside  in  the 
coating,  as  had  been  supposed,  but  in  the  glass ;  for 
after  a  phial  was  charged,  he  removed  the  coating,  and 
found  that,  by  applying  a  new  one,  the  shock  might  be 
received. 

From  these  facts,  Franklin  proposed  to  distinguish 
the  two  opposite  electrical  states  by  the  terms  plus  and 
minus,  or  positive  and  negative.  Thus,  when  a  body 
or  surface  has  more  than  its  usual  portion  of  electri- 
city, it  is  said  to  be  positively  electrified  ;  when  it  has 
less  than  its  usual  share,  it  is  said  to  be  negatively 
electrified.  These  two  conditions  exercise  a  constant 


ELECTRICITY.  165 

effort  to  balance  each  other  ;  and  when  a  communica- 
tion is  made  by  a  conducting  substance  between  two 
bodies  or  surfaces,  in  these  conditions,  a  discharge 
ensues,  and  equilibrium  is  restored.  Another  theory 
was  broached  by  M.  Du  Fay,  according  to  which  there 
are  two  electric  fluids,  the  one  called  vitreous  and  the 
other  resinous,  which  attract  each  other  after  separa- 
tion ;  but  the  theory  of  Franklin  has  prevailed,  and  the 
phraseology  introduced  by  him  is  the  only  one  used  in 
treating  of  the  science. 

The  preceding  view  of  the  subject  induced  Frank- 
lin to  suppose  that,  if  the  insides  of  several  Ley- 
den  jars  were  connected  by  means  of  a  conducting 
substance,  and  their  outsides  connected  with  each 
other  in  like  manner,  they  would  receive  and  impart  a 
charge  like  a  single  jar ;  that  the  shock  would  be  in- 
creased in  proportion  to  their  number,  and  thus  a  bat- 
tery of  any  force  would  be  obtained.  Accordingly 
they  were  soon  constructed  of  sufficient  power  to 
kill  small  animals.  Franklin  did  not  stop  here,  but 
pursued  his  researches  with  a  success  that  astonished 
the  world.  In  the  year  1749,  he  suggested  an  explana- 
tion of  the  phenomena  of  thunder-gusts,  and  of  the 
aurora  borealis,  on  electrical  principles.  He  pointed 
out  many  particulars  in  which  lightning  and  electricity 
agree  ;  and,  in  adverting  to  the  power  of  pointed  rods  in 
drawing  off  lightning,  he  supposed  that,  when  fixed  in 
the  air  at  the  time  when  the  atmosphere  was  charged 
with  lightning,  they  might,  without  noise  or  danger, 
draw  from  it  the  matter  of  the  thunderbolt  into  the 
body  of  the  earth.  The  manner  in  which  he  proposed 
to  bring  his  speculations  to  trial  was,  to  erect  on  the  top 


166  ELECTRICITY. 

of  a  tower,  or  other  elevated  place,  a  sentry-box,  from 
which  might  rise  a  pointed  iron  rod,  insulated  by  being 
fixed  in  a  cake  of  resin.  Electrified  clouds  passing 
over  this  would,  he  conceived,  impart  to  it  a  portion  of 
their  electricity,  which  would  be  rendered  evident  by 
the  sparks  it  yielded  on  being  touched  by  any  con- 
ductor. Philadelphia  contained  at  that  time  no  build- 
ing  which  Franklin  deemed  proper  for  his  purpose  ; 
he  therefore  laid  aside  the  thoughts  of  realizing  his 
conjecture  at  that  time.  But  while  he  thus  postponed 
the  completion  of  his  views,  they  were  actually  car- 
ried into  effect  in  France,  and  caused  incredible  sur- 
prise and  admiration. 

Franklin  had  communicated  to  his  friend  Collinson, 
in  England,  regular  accounts  of  his  experiments  and 
theories ;  and  the  latter  had  communicated  them  to  the 
public.  These  publications  were  widely  circulated, 
and  translated  into  different  languages.  In  France,  the 
principles  of  Franklin,  and  several  of  the  experiments 
by  which  they  were  supported,  soon  became  familiar 
to  some  of  the  chief  men  of  science,  and  his  proposed 
scheme  for  drawing  lightning  from  the  clouds  was  ac- 
tually accomplishe.d  in  the  year  1752.  A  month  after 
this,  but  before  any  intelligence  of  it  had  reached 
America,  Franklin  himself  had  demonstrated  the 
truth  of  his  theory  by  an  invention  of  his  own.  He 
prepared  a  silken  kite,  with  a  pointed  iron  at  the  top, 
communicating  with  the  string,  to  which,  at  the  lower 
end,  was  attached  a  key.  Having  raised  the  kite  into 
the  air  while  a  thunder-storm  was  approaching,  he 
held  it  by  a  band  of  silk  attached  to  the  key.  As  the 
cloud  passed  over  it,  he  beheld  the  fibres  of  the  string 


ELECTRICITY.  167 

suddenly  bristle  up,  and,  holding  his  knuckle  to  the  key, 
he  received  a  strong  electric  spark.  As  soon  as  the 
string  became  wet,  the  supply  of  electricity  was  co- 
pious. He  afterwards  prepared  an  insulated  iron  rod, 
to  draw  the  lightning  into  his  house,  and  by  means  of 
real  lightning  he  performed  all  the  experiments  usually 
executed  by  common  electrical  machines.  In  this  dis- 
covery the  French  had  the  precedence  in  point  of  time, 
but  they  had  only  followed  in  the  path  which  Franklin 
explicitly  pointed  out. 

Upon  the  public  announcement  of  this  discovery,  the 
experiment  was  repeated  in  various  parts  of  Europe, 
and  the  consequences  were  such  as  occasioned  alarm 
and  terror.  Many  persons  who  incautiously  attempted 
to  bring  down  the  ethereal  fire  suffered  much  by 
violent  shocks,  while  they  incurred  the  most  imminent 
danger.  In  one  instance,  a  fatal  catastrophe  ensued. 
On  the  6th  of  August,  1753,  Professor  Richman,  of  St. 
Petersburg,  was  making  experiments  on  lightning  drawn 
into  his  own  room.  He  had  provided  himself  with  an 
instrument  for  measuring  the  quantity  of  electricity 
communicated  to  his  apparatus ;  and  as  he  stood  with 
his  head  inclined  to  it,  his  attendant  observed  a  globe  of 
blue  fire,  as  large  as  his  fist,  jump  from  the  instrument, 
which  was  about  a  foot  distant,  toward  his  head.  Rich- 
man was  instantly  killed,  and  the  attendant  was  much 
hurt  The  latter  could  give  no  particular  account  of 
the  way  in  which  he  was  affected ;  for  at  the  time  the 
professor  was  struck,  he  stated  that  there  arose  a  sort  of 
steam  or  vapor  which  entirely  benumbed  him,  and  made 
him  sink  down  to  the  ground,  so  that  he  did  not  even 
hear  the  clap  of  thunder,  which  was  very  loud.  The 


168  ELECTRICITY. 

globe  of  fire  was  attended  with  an  explosion  like  that  of 
a  pistol ;  the  electrical  instrument  was  broken  to  pieces, 
and  the  fragments  were  thrown  about  the  room.  A 
red  spot  appeared  on  the  forehead  of  the  dead  body, 
and  a  blue  spot  on  the  foot,  from  which  the  shoe  had 
been  torn ;  whence  it  was  inferred  that  the  lightning 
had  entered  at  the  head,  and  passed  off  at  the  foot. 
On  the  back  of  the  attendant's  coat  appeared  long, 
narrow  streaks,  as  if  red-hot  wires  had  burnt  off  the 
nap. 

Common  electrical  experiments,  however,  are  per- 
fectly safe,  provided  an  ordinary  degree  of  caution  is 
observed.  A  great  multitude  of  devices  may  be  re- 
sorted to  for  showing  the  singular  properties  of  elec- 
tricity. The  artificial  aurora  borealis  may  be  ex- 
hibited in  the  following  manner.  Take  a  glass  phial, 
m  shape  and  size  like  a  Florence  flask,  with  a  stop- 
cock fitted  to  it.  Place  it  under  the  receiver  of  an  air- 
pump,  exhaust  the  air,  and  close  the  phial.  Rub  the 
glass  in  the  usual  manner  for  exciting  electrics,  and 
it  will  immediately  appear  luminous  within,  and  a 
flashing  light  will  be  observed,  forming  a  striking  min- 
iature resemblance  of  the  northern  lights.  The 
phial  may  be  made  luminous  by  holding  it  in  the  hand, 
with  one  end  presented  to  the  prime  conductor  of  an 
electrical  machine  :  the  strong,  flashing  light  which  then 
appears  will  remain  for  some  time  after  it  is  with- 
drawn ;  and  even  after  several  hours  have  elapsed,  on 
grasping  the  phial  with  the  hand,  strong  flashes  of  light 
will  reappear. 

If  a  bundle  of  hair  or  feathers  be  hung  upon  the 
prime  conductor,  the  moment  they  are  electrified,  by 


ELECTHICITY.  169 

working  the  machine,  they  begin  to  repel  and  fly  from 
one  another,  and  will  not  again  collapse  until  the  elec- 
tricity is  taken  off.  A  fanciful  mode  of  showing  this 
experiment  consists  in  making  the  form  of  a  human 
head,  with  hair  on  it ;  and,  upon  placing  this  image  up- 
on the  electrified  conductor,  the  hair  immediately  shoots 
up  "  like  quills  upon  the  fretful  porcupine."  If  two  per- 
sons—  one  standing  on  an  insulated  stool,  and  com- 
municating with  the  prime  conductor,  while  the  other 
stands  upon  the  floor  —  hold  in  their  hands  plates  of 
metal  in  such  a  manner  that  the  flat  sides  shall  be 
opposite  to  each  other  at  the  distance  of  about  two 
inches,  — on  strongly  electrifying  the  insulated  person, 
dense  and  frequent  flashes  will  be  observed  between 
the  plates,  forming  a  kind  of  artificial  lightning. 

Insulate  two  bodies,  and  charge  one  of  them  plus, 
and  the  other  minus  ;  then  suspend  between  them,  by 
a  silken  string,  an  artificial  spider,  of  which  the  body 
may  be  cork,  and  the  legs  the  fibres  of  feathers  ;  the 
spider  will  move  from  the  one  to  the  other,  till  their 
charge  is  equalized.  Place  a  cap  or  covering  of  metal 
upon  the  two  extremities  of  a  glass  tube,  four  or  five 
inches  long,  and  enclose  in  the  tube  some  sawdust  or 
pith-balls ;  then  charge  one  of  the  plates  plus,  and  the 
other  minus ;  when,  as  glass  is  a  non-conductor,  the 
equilibrium  can  be  restored  only  by  the  sawdust  or 
balls,  which  will  accordingly  jump  up  and  down,  till 
the  charge  of  each  plate  is  the  same.  To  illuminate 
water,  connect  one  end  of  a  chain  with  the  outside  of 
a  charged  jar,  and  let  the  other  end  lie  upon  the  table ; 
place  the  end  of  another  piece  of  chain  at  the  distance 
of  about  a  quarter  of  an  inch  from  the  former ;  then 
xui. — 15 


170  ELECTKICITV. 

set  a  decanter  of  water  upon  these  separated  ends, 
and,  on  making  the  discharge,  the  water  will  be  illu- 
minated. 

Every  one  knows  the  use  of  lightning-rods,  which, 
by  means  of  their  sharp  points  at  the  top,  draw  off 
gradually  the  electric  matter  in  the  clouds,  and  convey 
it  to  the  earth,  where  it  is  dissipated.  Personal  security 
during  a  thunder-storm  forms  another  important  object 
of  consideration.  Franklin  advises  persons  apprehen- 
sive of  lightning  to  sit  in  the  middle  of  the  room,  not 
near  a  metal  chandelier,  or  any  other  conductor,  and 
to  lay  their  feet  in  a  chair.  A  precaution  of  this  kind 
is  the  easiest  that  can  be  observed,  and  insures  a  high 
degree  of  safety.  It  will  be  still  safer  to  lay  two  or 
three  beds  or  mattresses  in  the  middle  of  the  room,  and, 
folding  them  double,  to  place  the  chairs  upon  them, 
A  hammock,  suspended  by  silken  cords,  would  be  an 
improvement  even  upon  this  apparatus.  The  floor 
should  be  dry,  or  the  lightning,  if  it  strikes  the  house, 
will  fly  all  over  the  room.  As  the  walls  and  floors 
of  houses  are  usually  dry,  and  therefore  non-con- 
ductors, the  lightning  is  prevented  from  spreading,  and 
seizes  with  the  more  avidity  the  slightest  articles  of 
metal  in  its  way.  A  person  has  been  known  to  be 
struck  dead  by  having  his  head  near  a  bell-wire  during 
a  thunder-storm.  Even  the  electricity  conducted  by 
the  gilding  of  a  picture-frame  would  be  highly  dan- 
gerous. Dr.  Priestley  observes,  that  the  safest  place  is 
the  cellar,  and  especially  the  middle  of  it ;  for  when  a 
person  is  lower  than  the  surface  of  the  earth,  the  light- 
ning must  strike  the  earth  before  it  can  reach  him  ;  it 
is  therefore  most  probable  that  it  will  become  imme- 


ELECTRICITY. 


171 


diately  diffused,  and  not  enter  the  cellar,  especially  if  it 
be  dry. 

The  best  situation  for  a  person  who  happens  to  be 
in  the  fields  during  a  thunder-storm  is  within  a  short 
distance  of  a  tree,  but  not  immediately  under  it,  as  the 
lightning  generally  strikes  first  the  highest  and  best 
conductors.  The  frequency  with  which  barns  in  the 
country  are  struck  by  lightning  has  been  the  subject 
of  much  remark ;  it  seems  not  unlikely  that,  from  their 
contents  of  fresh  hay,  grain,  and  other  matters,  they 
are  constantly  sending  upward  a  column  of  vapor, 
which  may  serve  as  a  conductor  to  bring  down  the 
electric  fluid.  It  would  appear,  therefore,  that  they 
are  unsafe  places  of  shelter  when  there  is  lightning  .n 
the  atmosphere. 


GALVANISM. 


THIS  science  is  a  branch  of  natural  philosophy  which 
has  originated  within  a  few  years,  and  derives  its  name 
from  Galvani,  a  professor  of  anatomy  at  Bologna,  in 
Italy.  He  had  the  good  fortune  to  make  some  observa- 
tions on  the  electricity  of  the  muscles  of  frogs,  which  ap- 
peared to  him  to  depend  on  a  new  power  in  the  animal 
body  ;  and  although  it  is  now  generally  admitted  that  he 
drew  an  erroneous  inference  from  his  observations,  yet 
they  led  to  a  train  of  experiments  which  have  associated 
his  name  with  some  of  the  most  brilliant  discoveries  of 
modern  science.  To  this  supposed  new  power  he  gave 
the  name  of  animal  electricity,  conceiving  it  to  depend 
upon  something  inherent  in  the  animal  body  itself;  but 
we  now  regard  these  effects  as  produced  by  minute 
quantities  of  the  electric  fluid  set  at  liberty  by  a  certain 
agency  of  substances  upon  each  other. 

The  original  discovery  took  place  by  accident.  The 
wife  of  Galvani,  being  in  ill  health,  employed,  as  a 
restorative,  frog-soup,  according  to  the  custom  in  that 
country.  A  number  of  these  animals,  skinned  for  the 
purpose  of  cooking,  chanced  to  lie  near  an  electrical 
machine.  While  the  machine  was  in  action,  an  at- 
tendant happened  to  touch,  with  the  point  of  a  scalpel, 
the  thigh  of  one  of  the  frogs,  when  it  was  observed 
that  the  muscles  of  the  limb  were  instantly  thrown  into 


GALVAX1SM.  173 

strong  convulsions.  This  experiment  was  performed 
in  the  absence  of  the  professor,  but  it  was  noticed  by 
his  wife,  who  communicated  it  to  her  husband.  He 
repeated  the  experiment,  varied  it  in  different  ways, 
and  perceived  that  the  convulsions  took  place  only 
when  a  spark  was  drawn  from  the  prime  conductor, 
while  the  nerve  of  the  thigh  was  at  the  same  time 
touched  with  a  substance  which  was  a  conductor  of 
electricity.  When  a  frog  was  so  placed  as  to  form  a 
part  of  an  electric  circuit,  it  was  found  that  an  ex- 
tremely minute  quantity  of  electricity  produced  con- 
vulsions in  the  muscles :  if  the  hind  legs  were  dissected 
from  the  body,  —  the  connection  being  kept  up  by  the 
crural  nerves  only,  —  and  the  electric  fluid  was  passed 
through  it  in  this  state,  a  still  more  minute  quantity 
produced  a  visible  effect,  so  that  a  frog  prepared  in  this 
manner  was  capable  of  exhibiting  very  decisive  marks 
of  electricity,  when  none  could  be  detected  by  an 
electrometer. 

After  employing  the  electric  fluid  as  disengaged 
from  the  common  machine,  he  next  tried  the  atmos- 
pherical electricity ;  and  it  was  in  this  experiment  that 
he  was  first  led  to  observe  the  effects  of  galvanism, 
properly  so  called.  Having  suspended  a  number  of 
frogs  by  metallic  hooks  to  an  iron  railing,  he  found 
that  their  limbs  were  frequently  thrown  into  convul- 
sions when  it  did  not  appear  that  there  was  any  elec- 
tricity in  the  atmosphere.  Having  duly  considered 
this  phenomenon,  he  discovered  that  it  did  not  originate 
from  an  extraneous  electricity,  but  that  it  depended 
upon  the  position  of  the  animal  with  respect  to  certain 
metallic  bodies. 

15* 


174  GALVANISM. 

The  first  stage  or  epoch  in  the  history  of  galvanism 
must  be  considered  that  in  which  it  was  observed  that  ex- 
cited electricity  produced  muscular  contractions  in  dead 
animals ;  the  second  is  that  in  which  it  was  observed  that 
different  metallic  bodies,  by  mere  contact,  produced  the 
same  kind  of  contractions ;  the  third  and  most  remark- 
able one  commences  with  Volta's  admirable  discovery 
of  the  means  of  accumulating  the  galvanic  influence. 
This  invention,  which  justly  confers  so  much  celebrity 
on  its  author,  is,  in  galvanism,  analogous  to  that  of  the 
Leyden  phial  in  common  electricity  ;  and  became,  like 
the  phial,  the  precursor  of  the  most  brilliant  discoveries. 
We  can  form,  as  yet,  but  a  very  imperfect  judgment 
of  the  importance  of  the  consequences  to  which  it  will 
lead.  It  is  called  the  Voltaic  pile,  and  is  made  by 
combining  the  effects  of  a  number  of  plates  of  differ- 
ent metals,  by  which  means  a  galvanic  battery,  capa- 
ble of  giving  a  shock,  is  produced.  As  silver  and  zinc 
had  been  found  —  when  a  single  plate  of  each  was  em- 
ployed —  to  have  the  greatest  effect  in  producing  mus- 
cular contractions,  these  metals  were  selected  by  Volta 
for  his  battery.  The  silver  plates  generally  consisted 
of  coins,  and  the  plates  of  zinc  were  of  the  same  size. 
The  like  size  and  number  of  pieces  of  cloth,  paste- 
board, or  leather,  steeped  in  salt  water,  were  also  pro- 
vided. These  substances  were  piled  upon  each  other 
alternately,  and  the  whole  pile  was  supported  by  some 
non-conducting  substance. 

The  Voltaic  pile  is  now  but  little  used  in  its  original 
shape,  having  been  superseded  by  galvanic  batteries  of 
a  more  convenient  form,  particularly  when  a  great 
accumulation  of  galvanism  is  required.  The  pile  or 


GALVANISM.  175 

battery  is  fojnd  to  unite  the  effects  of  as  many  pair  of 
plates  as  it  contains.  A  pile  of  50  pair  will  give  a 
pretty  smart  shock,  similar  to  that  from  an  e'wtrical 
machine  when  touched  by  the  two  hands  f'^iultane- 
ously  at  the  two  extremities ;  but  little  or  no  shock  is 
perceived  unless  the  hands  are  moistened.  The  efiects 
are  also  increased  wheu  a  larger  surface  of  the  body 
is  exposed  to  action.  Thus,  if  the  communication  is 
made  by  touching  with  the  tips  of  the  fingers  only,  the 
effect  is  not  perceived  beyond  the  joints  of  the  knuc- 
kles ;  but  if  a  spoon  or  other  metallic  substance  be 
grasped  in  moistened  hands,  the  shock  is  felt  up  to  the 
shoulders.  If  the  communication  be  made  between 
any  part  of  the  face,  particularly  near  the  eyes,  and 
another  part  of  the  body,  a  vivid  flash  of  light,  corre- 
sponding with  the  shock,  is  perceived.  This  phenome- 
non may  be  more  faintly  observed  by  putting  a  piece 
of  silver  between  the  upper  lip  and  the  gum,  and  lay- 
ing a  piece  of  zinc  at  the  same  time  on  the  tongue ; 
upon  bringing  the  two  metals  into  contact,  a  faint  flash 
of  light  generally  appears.  It  is  singular  that  this 
light  is  equally  vivid  in  broad  day  as  in  the  dark,  and 
whether  the  eyes  be  shut  or  open. 

Frogs  have  been  found  the  most  convenient  subjects 
for  galvanic  operations.  Galvani  prepared  these  ani- 
mals by  skinning  their  legs  when  recently  dead,  and 
having  them  attached  to  a  small  part  of  the  spine, 
but  separated  from  the  rest  of  the  body.  Any  other 
limb  may  be  prepared  in  a  similar  manner,  by  depri- 
ving it  of  its  integuments,  and  laying  partly  bare  the 
nerve  which  belongs  to  it  The  strongest  contractions 
are  produced  when  the,  galvanic  electric'ty  is  made  to 


176  GALVANISM. 

pass  through  the  nerve  to  the  muscles.  Frogs  which 
have  been  galvanized  quickly  become  putrid.  Per- 
haps most  persons  who  try  galvanic  experiments  mere- 
ly for  the  purpose  of  amusement  would  choose  to  dis- 
pense with  the  operation  of  decapitating  and  skinning 
frogs.  We  may  therefore  observe  that  an  ample  proof 
of  the  power  of  galvanism  over  the  dead  muscle  may 
be  obtained  by  galvanizing  any  animal  killed  for  the 
kitchen.  It  will  be  necessary  only  to  point  the  wires 
from  the  battery,  and  to  penetrate  the  skin  with  them, 
at  the  two  parts  between  which  a  communication  is 
intended  to  be  made. 

Those  animals  only  which  possess  distinct  limbs  and 
muscles  can  be  convulsed  by  galvanism  ;  yet  reptiles 
may  be  affected  by  it.  Thus,  if  a  leech  or  worm  be 
laid  upon  a  plate  of  zinc,  and  surrounded  at  a  little  dis- 
tance by  half  dollars,  every  time  the  animal  touches 
one  of  the  pieces  of  silver,  it  will  be  observed  to  shrink 
back.  The  medical  uses  of  galvanism  cannot  yet  be 
fully  estimated.  In  some  cases,  it  has  proved  bene- 
ficial ;  in  others,  it  has  had  no  effect  whatever ;  and 
in  others  still,  an  unfavorable  effect  has  been  ascribed 
to  it.  The  cases  in  which  it  is  in  general  most  proper 
to  try  it,  are  those  in  which  common  electricity  has 
failed.  In  instances  of  numbness,  palsy,  and  suffoca- 
tion, it  has  proved  highly  advantageous. 

The  electricity  of  the  torpedo,  and  the  electrical  eel, 
has  a  considerable  resemblance  to  galvanism  ;  it  gives 
a  sensible  shock,  but  has  little  power  of  any  other  sort, 
and  might  be  well  imitated  by  a  vast  number  of  mi- 
nute plates  put  in  action  by  a  fluid  feeble  in  its  power 
of  oxidation. 


GALVANISM.  177 

The  history  of  science  affords  many  examples  of 
observations  which  have  remained  isolated  and  useless 
for  ages,  and  which,  though  often  denied  and  discredited, 
have,  by  the  progress  of  discovery,  grown  into  impor- 
tance, and  become  parts  of  a  beautiful  system  —  con- 
tribut'ng,  at  the  same  time,  essentially  to  the  early  ma- 
turity of  some  departments  of  knowledge.  Hence 
those  who  have  accurately  detailed  a  single  new  phe- 
nomenon, which  appeared  to  have  no  connection  with 
any  thing  useful  or  any  thing  known,  have,  in  fact,  often 
been  performing  a  work  which  should  give  celebrity  to 
their  names,  by  the  direction  which  it  has  given  to  in- 
quiry, and  the  light  it  has  afforded  to  subsequent  re- 
searches. In  galvanism,  several  instances  of  the  kind 
have  occurred,  and  some  of  them  are  so  curious  as  to 
deserve  mention. 

A  long  time  prior  to  the  establishment  of  galvanism 
as  a  science,  it  had  been  observed  that,  if  two  different 
metals  were  placed  in  contact  under  water,  they  were 
subject  to  a  rapid  oxidation,  though  the  water  had  no 
perceptible  action  upon  them  when  they  were  apart. 
It  had  also  been  observed  that  ancient  inscriptions 
made  of  mixed  metals  were  totally  defaced,  while 
those  made  of  pure  metals,  equally  old,  were  in  excel- 
lent preservation.  When  metals  have  been  soldered 
bv  means  of  other  metals,  they  were  found  to  contract 
a  tarnish  about  the  parts  where  they  were  joined  ;  and 
the  copper  sheathing  of  ships,  when  fastened  with  iron 
nails,  soon  corrodes  where  the  different  metals  are  in 
contact  It  had  been  generally  affirmed  that  porter 
drunk  out  of  a  pewter  vessel  had  a  taste  different  from 
that  drunk  out  of  glass  or  earthenware,  &c.  It  is  now 


178 


GALVANISM. 


evident  that,  in  all  these  cases,  the  effects  were  pro- 
duced by  galvanic  action. 

Several  persons  may  receive  the  galvanic  shock  to- 
gether, by  joining  hands,  in  the  same  manner  as  in 
receiving  the  shock  from  a  Leyden  jar.  Their  hands 
should  be  well  moistened ;  but,  unlike  electricity,  the 
strength  of  the  shock  diminishes  as  it  proceeds,  in  con- 
sequence of  which,  the  last  person  feels  it  much  less 
violently  than  the  first.  After  receiving  the  shock,  a 
slight  numbness  of  the  part  exposed  to  it  remains  for 
some  time.  The  shock  may  be  also  conveniently 
given  by  placing  the  hands  or  feet  in  salt  water,  and 
bringing  wires  from  each  end  of  the  battery  into  the 
liquid.  If  any  other  part  of  the  body  is  intended 
to  be  operated  upon,  a  sponge  moistened  with  salt 
water,  and  fastened  to  a  metal  plate  connected  with  one 
end  of  the  battery,  may  be  applied  to  the  part,  and  the 
hand  or  foot  put  into  a  vessel  of  the  same  liquid,  con- 
nected by  a  wire  with  the  other  end  of  the  battery. 

The  decomposition  of  water  by  galvanism  is  easily 
effected.  The  simplest  mode  of  performing  this  ex- 
periment is,  to  bring  the  wires  coming  from  each  end 
of  the  battery  into  a  vessel  of  water.  A  profusion  of 
bubbles  of  gas  will  appear  to  be  given  out  from  each 
wire  as  far  as  it  is  immersed  in  the  liquid.  The  closer 
the  wires  are  brought  together,  so  as  not  to  touch, 
the  more  rapidly  decomposition  goes  on.  The  gas 
produced  from  the  wire  coming  from  the  zinc  end  of 
the  battery,  if  the  wire  be  of  gold  or  platina,  will  be 
oxygen ;  but  if  the  wire  be  of  any  metal  more  oxidable, 
no  gas  will  appear,  but  the  wire  will  be  oxidated.  The 
gas  furnished  by  the  wire  from  the  copper  end  of  the 


GALVAXISM.  179 

battery,  of  whatever  metal  the  wire  may  be,  is  of  pure 
hjdrogen.  Both  the  gases  are  produced  by  the  decom- 
position of  the  water. 

Batteries  containing  6000  or  8000  square  inches 
of  zinc  and  copper  surface,  furnish  the  means  of  per- 
forming a  variety  of  experiments  in  which  light  and 
heat  are  abundantly  extricated.  Such  a  battery,  in  its 
highest  state  of  energy,  will  make  red-hot,  and  even 
fuse,  a  considerable  length  of  fine  steel  wire,  when  it 
forms  part  of  the  circuit  in  making  the  connection  be- 
tween the  two  ends  of  the  battery.  Attach  to  the  end 
of  each  wire  of  the  battery  a  small  piece  of  charcoal : 
on  completing  the  circuit,  by  bringing  the  two  pieces  of 
charcoal  into  contact,  a  light,  the  most  vivid  that  the 
eye  can  behold,  immediately  appears.  The  charcoal 
should  be  prepared  for  the  purpose  by  burning  some 
very  bard,  close-grained  wood  in  a  closed  vessel.  The 
foils,  or  thin  leaves,  of  gold,  silver,  tin,  and  other 
metals,  may  be  consumed  by  the  help  of  mercury. 
Let  the  conducting  wire  from  one  end  of  the  battery 
terminate  in  the  mercury,  in  a  small  iron  dish ;  to  the 
other  conducting  wire  attach  the  foil  or  wire  to  be 
deflagrated,  and,  upon  touching  the  mercury  with  the 
latter,  the  effect  will  follow.  The  light  afforded  by  the 
combustion  of  different  metals  is  of  different  colors. 
Copper  or  brass  leaf,  commonly  called  Dutch  gold^ 
burns  with  a  green  light ;  silver  with  a  pale  blue  light; 
gold  with  a  yellow  light ;  and  all  with  a  slight  crackling. 
The  galvanic  discharge  fires  gunpowder,  hydrogen  gas, 
oils,  alcohol,  &c. 

One  of  the  most  brilliant  discoveries  in  modern 
chemistry  was  effected  by  the  application  of  galvanism. 


180  GALVANISM. 

This  was  the  decomposition  of  the  fixed  alkalies,  by  Sir 
Humphry  Davy.  These  alkalies — namely,  soda  and 
potass  —  were  supposed  to  be  simple  bodies  ;  but  Davy 
discovered  them  to  be  metallic  oxides.  A  small  piece 
of  one  of  these  oxides  being  laid  upon  a  piece  of  plat- 
ina  connected  with  one  end  of  a  powerful  battery,  and 
another  piece  of  platina,  connected  with  the  other  end 
of  the  battery,  being  brought  into  contact  with  it,  a 
portion  of  black  matter  is  soon  formed,  in  which  are 
found  imbedded  small  metallic  globules.  These  glob- 
ules are  the  base  of  the  alkali,  which  has  been  de- 
prived of  its  oxygen  by  the  action  of  the  battery.  Ex- 
periments made  by  Davy,  and  other  chemists,  also 
showed  that  many  other  substances  before  supposed  to 
be  simple  —  as  lime,  barytes,  strontites,  magnesia,  zir- 
con, &c. — were  capable  of  analysis;  and  though  silex, 
alumina,  and  others,  offered  great  resistance  to  the  appli- 
cation of  galvanism,  in  the  majority  of  cases  the  anal- 
ysis was  successful.  In  giving  a  theory  of  galvanism, 
we  are  struck  with  a  primary  question :  How  does 
galvanism  differ  from  common  electricity  ?  This 
query  may  refer  both  to  the  nature  of  the  phenomena 
themselves,  and  to  the  means  employed  for  their  pro- 
duction. It  is  in  some  cases  difficult  to  draw  the 
exact  line  of  distinction  between  the  two  principles, 
and  many  persons  doubt  whether  any  precise  distinc- 
tion actually  exists.  For,  as  it  is  conceived  that  they 
both  depend  upon  the  same  agent,  having  merely  ex- 
perienced some  modification  in  its  nature,  or  mode  of 
action,  we  must  conclude  that  there  may  be  some  inter- 
mediate or  indeterminate  state  which  might  be  referred 
to  the  one  or  the  other  with  almost  equal  propriety. 


GALVANISM. 


181 


The  electricity  produced  by  the  galvanic  battery  is  of 
the  same  nature  as  that  given  by  the  common  electrical 
machine ;  the  only  difference  being  that  the  mode  of 
producing  galvanism  is  continuous ;  that  is,  when  in 
any  way  discharged,  it  is  immediately  reproduced  by 
the  oxidation  of  the  zinc ;  and  hence  many  galvanic 
phenomena  have  been  successfully  imitated  by  a  series 
of  sparks  of  ordinary  electricity. 


• 

91O 

• 


xm.— 16 


MAGNETISM. 


THE  word  MAGNETISM,  in  its  original  and  particular 
acceptation,  is  employed  to  denote  that  invisible  force 
with  which  certain  ores  of  iron,  called  in  Greek  mag- 
nes,  attract  pieces  of  iron  to  themselves.  This  prop- 
erty is  found  naturally  in  all  the  ores  of  oxidulated 
iron  ;  but  when  the  laws  of  its  action  are  known,  we 
may  excite  it  artificially  in  metallic  iron  or  steel  by  a 
particular  process.  Of  the  nature  of  the  principle 
which  produces  the  phenomena  of  magnetism,  we  are 
entirely  ignorant. 

Of  magnets  there  are  two  kinds  —  the  natural  and  the 
artificial.  The  natural  magnet,  or  loadstone,  is  an  ore 
of  iron,  hard  enough  to  strike  fire  with  steel :  its  color 
is  dull,  generally  dark  gray,  brown,  or  nearly  black. 
The  power  of  magnetic  attraction  may  be  communi- 
cated to  iron  in  any  state  ;  and  a  bar  of  iron  possessing 
it  in  any  considerable  degree  is  called  an  artificial 
magnet.  Magnetism  is  an  accidental  property  of  iron, 
and  the  metal  may  either  possess  or  be  deprived  of  it 
without  losing  any  of  its  essential  characteristics  as  a 
metal.  Magnetic  attraction  was,  till  lately,  supposed  to 
be  exerted  by  ferruginous  bodies  alone  on  other  ferru- 
ginous bodies,  and  hence  the  use  of  the  magnet  was 
resorted  to  as  a  sure  means  of  detecting  the  presence 


MAGNETISM.  183 

of  iron ;  but  modern  investigations  have  shown  that 
nickel  is  also  susceptible  of  it ;  cobalt  is  likewise  sup- 
posed to  be  magnetic. 

A  magnet  suspended  by  a  thread,  or  placed  in  any 
situation  that  leaves  it  at  liberty  to  move  with  freedom, 
turns  one  end  toward  the  north.  The  two  ends  of  a 
magnet  are,  therefore,  called  its  poles;  they  are  not 
reversible  points,  but  the  pole  which  is  at  any  time  ob- 
served to  point  toward  the  north  will  always  point  in 
the  same  direction,  or  nearly  so.  The  attractive  prop- 
erties of  the  magnet  have  been  known  from  time  im- 
memorial, and  its  polarity  was  known  in  Europe  as 
early  as  the  middle  of  the  12th  century.  Of  course 
there  is  no  ground  for  the  current  belief  that  the  mari- 
ner's compass  was  invented  by  Gioja  of  Amalfi,  in  the 
14th  century.  It  is  pretty  satisfactorily  ascertained 
that  the  Chinese  had  compasses  long  before  the  Chris- 
tian era ;  but  although  the  use  of  them  on  land  was 
common,  they  do  not  appear  to  have  been  applied  to 
the  purposes  of  navigation  till  the  3d  or  4th  century, 
when  they  are  distinctly  mentioned  in  the  Chinese  his- 
tories. That  the  Europeans  derived  the  compass  from 
the  East,  is  evident  from  the  fact,  that  it  was  known 
on  the  coast  of  Syria  before  it  appeared  in  Europe, 
whither  it  was  undoubtedly  carried  by  the  crusaders. 
The  first  distinct  mention  of  it  in  Europe  is  in  a 
satire,  written  by  Guyot  de  Provins,  about  the  year 
1190.  The  French,  in  consequence,  lay  claim  to  the 
discovery  of  the  compass ;  and  this  notion  has  been 
strengthened  by  the  circumstance  of  the  north  pole 
being  marked  on  the  card  with  a  fleur  de  lis ;  but  this 
figure  is  supposed  to  be  only  an  ornamented  cross. 


184  MAGNETISM. 

The  most  simple  method  of  exhibiting  the  power 
and  distribution  of  magnetism,  in  a  piece  of  natural 
loadstone,  is  to  roll  it  in  the  filings  of  iron :  on  taking 
it  out,  it  will  be  perceived  that  the  filings  have  accu- 
mulated at  the  two  ends  of  the  loadstone,  leaving  the 
middle  comparatively  bare.  If  we  examine  these 
crests  of  filings  attached  to  the  poles  of  the  loadstone, 
we  shall  observe  that  they  radiate  by  adhering  end 
to  end  to  one  another.  This  phenomenon  is  particu- 
larly deserving  of  attention,  as  it  informs  us  that  iron, 
placed  in  contact  with  a  loadstone,  becomes  itself 
magnetic,  in  the  same  manner  that  an  insulated  body 
becomes  electric  when  held  in  the  presence  of  another 
body  that  is  electrified. 

Magnetism  may  be  communicated  to  a  bar  of  steel  in 
a  more  prompt  and  energetic  manner  by  two  loadstones 
than  by  one,  by  placing  its  two  extremities  in  contact, 
at  the  same  time,  with  the  contrary  poles  of  the  load- 
stones. The  same  loadstone  may  thus  successively 
render  magnetic  any  number  of  bars,  without  losing 
any  portion  of  its  original  virtue  ;  from  which  it  is 
evident  that  it  communicates  actually  nothing  to  the 
bars,  but  only  develops,  by  its  influence,  some  hidden 
principle.  In  the  same  manner,  a  stick  of  sealing-wax, 
when  rubbed,  loses  nothing  of  its  electricity  by  the 
decomposition  which  its  influence  effects  at  a  distance 
in  the  natural  electricities  of  other  bodies. 

When  we  hold  one  of  the  poles  of  a  loadstone  at  a 
distance  from  a  magnetic  needle,  suspended  horizontally 
by  its  centre,  the  two  poles  of  the  loadstone  act  at  once 
upon  the  needle,  but  the  action  of  the  nearest  pole  is 
always  the  strongest.  The  needle  then  turns  toward 


MAGXETISX.  100 

Die  loadstone  the  pole  which  is  attracted,  and  keeps  at 
a  distance  the  one  which  is  repelled.  If,  after  it  has 
taken  a  position  of  equilibrium,  we  turn  it  ever  so  little 
from  its  place,  it  will  return  to  it  by  a  series  of  oscilla- 
tions, in  the  same  manner  as  a  pendulum,  pushed  from 
the  perpendicular  line,  will  return  to  it  by  the  influence 
of  gravity.  A  motion  absolutely  similar  to  this  is 
observed  in  magnetic  needles,  freely  suspended,  when 
they  are  pushed  ever  so  little  out  of  the  magnetic  me- 
ridian. From  this  circumstance,  therefore,  as  well  as 
from  the  constant  direction  which  it  gives  them,  it  ap- 
pears that  the  terrestrial  globe  acts  upon  them  exactly 
like  a  true  magnet.  Whether  this  faculty  is  owing  to 
the  mines  of  iron  and  magnetic  substances  which  it 
contains,  or  whether  it  depends  upon  some  other  cause, 
we  are  yet  ignorant 

The  directive  property  of  the  magnet  is  one  of  the 
most  important  discoveries  ever  made  by  man.  It 
gives  to  navigators  an  infallible  guide  to  point  their 
course  across  the  trackless  ocean,  in  the  midst  of  the 
darkest  nights,  and  when  fogs  or  tempests  have  entirely 
obscured  the  heavens :  a  magnetic  needle,  balanced 
upon  a  pivot,  points  out  to  them  the  fixed  direction  in 
which  they  ought  to  keep,  and  this  valuable  indication 
conducts  them  as  accurately  as  even  the  observation  of 
the  stars.  Previous  to  this  invention,  so  useful  and 
simple,  the  seaman  could  not  venture  to  a  distance  from 
the  coast  The  discovery  of  the  compass  has  given 
him  the  means  of  launching  into  the  farthest  depths  of 
the  ocean,  and  of  seeking  regions  unknown  to  the  most 
powerful  and  enlightened  nations  of  antiquity. 

The  magnetic  needle  does  not,  in  general,  point 
16* 


186  MAGNETISM. 

exactly  north  and  south ;  and  this  deviation,  which  is 
different  in  different  parts  of  the  globe,  and  is  even 
different  according  to  the  hour  of  the  day,  was  first 
observed  by  Columbus  on  his  voyage  of  discovery  to 
America,  in  1492.  The  phenomenon  caused  great 
alarm  at  the  time,  for  it  was  feared  that  the  only  guide 
which  the  mariner  possessed,  to  conduct  him  across  the 
trackless  waste,  was  about  to  fail  him.  Succeeding 
observations,  however,  have  shown  that  this  irregularity 
is  subject  to  certain  laws,  and  that  the  earth  has  a 
magnetic  pole,  which  does  not  exactly  correspond  to 
the  rotatory  pole.  The  aberration  from  the  true  north 
and  south  line  is  called  the  variation  of  the  compass. 
It  occurs  at  different  hours  of  every  day,  and  at  differ- 
ent seasons  of  the  year,  but  it  is  not  exactly  periodical. 
It  is  also  very  observable  at  the  time  of  the  appearance 
of  the  northern  lights.  The  greatest  variation  from 
the  north  toward  the  west  takes  place  about  2  o'clock 
in  the  afternoon,  and  the  nearest  approach  of  the  needle 
to  the  pole  is  about  8  in  the  morning.  The  needle  has 
an  annual  progress,  between  January  and  March,  toward 
the  west ;  between  March  and  May  it  returns  toward 
the  north ;  in  June  it  is  stationary ;  in  July  it  varies 
again  to  the  west ;  in  August,  September,  and  October, 
it  returns  again  toward  the  pole,  and  during  the  re- 
mainder of  the  year  it  varies  westerly.  Before  vol- 
canic eruptions  and  earthquakes,  the  needle  is  often 
subject  to  extraordinary  agitations.  Before  1657,  the 
variation  was  easterly  ;  during  that  year,  the  needle 
pointed  due  north ;  and  the  variatkn  to  the  west  has 
constantly  increased  ever  since. 

The  magnetic  needle  is  also  subject  to  an  influence 


MAGNETISM.  187 

called  the  dip.  When  a  bar  of  iron  unmagnetized  is 
balanced  in  an  exact  horizontal  position,  and  the  mag- 
netism is  afterwards  applied,  the  north  pole  of  the 
magnet  will  dtp,  or  point,  below  the  horizon.  This 
movement  varies  in  different  latitudes ;  in  the  southern 
hemisphere,  it  is  the  south  pole  of  the  magnet  which 
dips  ;  at  the  equator  there  is  hardly  any  dip. 

Magnetism  is  transmitted  through  all  bodies ;  and, 
apparently,  through  those  which  are  the  most  solid  with 
as  much  ease  as  through  the  most  porous.  In  moving 
a  magnet  to  and  fro,  under  a  slice  of  cork  or  a  plate 
of  gold,  the  effect  upon  bits  of  iron  lying  upon  these 
substances  appears  to  be  the  same ;  and  no  difference 
is  observed  whether  magnetical  experiments  are  tried 
in  ractto,  or  in  the  open  air.  But  there  are  other 
causes  which  render  magnetism  one  of  the  most  mu- 
table of  powers.  It  is  weakened  by  an  increase  of 
temperature  ;  and  a  white  heat  almost  entirely  erad- 
icates it. 

Magnetic  repulsion  takes  place  only  between  poles 
of  the  same  name.  Thus  a  north  pole  always  repels 
a  north  pole,  and  a  south  pole  repels  a  south  pole  :  yet 
it  is  observed  that,  when  the  north  pole  of  a  weak 
magnet  is  presented  to  the  north  pole  of  a  powerful 
one,  an  attraction  often  appears.  But  when  this  occurs, 
it  is  found  that  the  poles  of  the  weaker  magnet  have  in 
reality  been  reversed.  The  middle  part  of  a  magnet, 
exactly  between  the  extremities  of  the  poles,  possesses 
no  power  either  of  attraction  or  repulsion ;  but  if  the 
magnet  be  divided  in  the  middle,  each  half  will  be- 
come a  distinct  magnet ;  and  those  parts  which  were 
the  north  and  south  poles  of  the  single  original  magnet 


188 


MAGNETISM. 


will  still  retain  their  character.  The  position  in  which 
a  magnet  is  kept,  and  the  manner  in  which  it  is  loaded, 
nave  an  effect  upon  its  power.  If  it  be  constantly  kept 
with  its  pole  to  the  north,  and  be  loaded  with  a  weight 
which  is  gradually  increased,  it  acquires  additional 
magnetism.  But  in  proportion  as  its  position  deviates 
from  the  pole,  and  if  at  the  same  time  it  is  kept  with 
little  or  no  weight  upon  it,  the  magnetical  power  is  soon 
materially  impaired. 

In  the  northern  hemisphere,  the  north  pole  of  a  mag- 
net is  considered  the  most  powerful ;  in  the  southern 
the  south  pole  predominates.  But,  in  order  to  render  a 
magnet  capable  of  raising  the  greatest  weight  possible, 
an  artifice  is  adopted  to  render  both  poles  active  in 
lifting  the  same  load.  This  is  done,  in  what  is  called 
the  horse-shoe  magnet,  by  bending  the  bar  into  a  horse- 
shoe till  the  two  poles  nearly  touch.  By  combining 
many  bars  into  one  magnet,  an  enormous  power  may 
be  obtained.  Magnets  of  this  sort  are  used  by  artisans 
to  touch,  or  magnetize,  compass-needles.  A  magnet 
employed  in  the  communication  of  magnetism  rather 
gains  than  loses  in  strength,  but  it  cannot  impart  a 
greater  degree  of  power  than  its  own.  Every  kind  of 
violent  percussion,  or  whatever  disturbs  or  deranges  the 
disposition  of  the  particles  of  a  magnet,  weakens  its 
power.  A  strong  magnet  has  been  entirely  deprived 
of  its  magnetism  by  several  smart  strokes  of  a  hammer. 
The  effect  of  the  hammer  is  in  some  measure  corre- 
spondent to  what  takes  place  in  the  tube-magnet.  A 
glass  tube  filled  with  iron  filings  may  be  magnetized 
like  a  steel  bar,  and  become  a  perfect  magnet ;  but 
when  the  situation  of  the  filings  among  themselves  is 


MAGNETISM.  189 

altered  by  shaking  the  tube,  the  magnetism  disap- 
pears. 

In  some  instances,  magnetism  may  be  obtained  with- 
out the  agency  of  a  magnet  Thus,  if  a  bar  of  iron, 
three  or  four  feet  long,  be  held  in  a  vertical  position,  or, 
what  is  more  proper,  in  the  direction  of  the  dipping- 
needle,  it  will  immediately  show  signs  of  magnetism, 
by  attracting  light  pieces  of  iron.  The  lower  end  of 
the  bar  will  be  the  north  pole ;  but  if  the  bar  be  in- 
verted, the  pole  will  change  likewise.  On  the  south 
side  of  the  equator,  the  lower  extremity  is  always  the 
south  pole.  To  succeed  in  this  experiment,  the  iron 
should  be  soft.  Bars  of  iron  which  have  for  a  long 
time  remained  entirely  or  for  the  most  part  in  a  vertical 
position  —  as  fire-irons,  bars  of  windows,  <fcc.  —  are  gen- 
erally found  to  be  more  or  less  magnetical.  If  a  long 
piece  of  iron  be  made  red-hot,  and  then  left  to  cool  in  the 
direction  of  the  dipping-needle,  it  becomes  magnetical. 
It  has  been  observed  that  to  strike  a  magnet  with  a 
hammer  may  deprive  it  of  its  magnetism :  on  the  other 
hand,  it  is  found  that  if  a  magnetical  bar  be  struck  with 
a  hammer,  or  rubbed  with  a  file,  while  held  in  the  posi- 
tion of  the  dipping-needle,  it  will  acquire  magnetism. 
An  electrical  shock  produces  the  same  effect,  and  light- 
ning often  renders  bars  of  iron  magnetic ;  but  both 
lightning  and  the  electric  shock  will  destroy  the  power 
of  magnets  already  formed. 

A  circular  piece  of  iron,  like  the  verge  of  a  watch, 
may  have  a  north  or  south  pole ;  and  when  the  verge 
of  a  watch  happens  to  acquire  magnetism,  its  constant 
tendency  to  one  direction  has  a  material  influence  on 
the  performance  of  the  machine.  A  watch  which 


190  MAGNETISM. 

• 

moved  incorrectly  with  a  steel  verge,  kept  perfect  time 
when  a  gold  one  was  substituted,  and  the  steel  verge, 
on  trial,  was  found  to  possess  polarity.  This  fact  is  an 
important  one  to  watch-makers,  who  sometimes  are 
unable  to  discover  the  cause  of  the  defective  movement 
in  a  watch  that  appears  to  be  in  perfect  order. 

Many  ingenious  theories  of  magnetism  have  been 
broached  by  men  of  science  ;  but  the  only  proposition 
concerning  it  which  seems  placed  beyond  the  reach  of 
doubt  is,  that  the  earth  itself  acts  as  a  great  magnet ; 
and  if  this  be  evident,  it  will  scarcely  be  denied  that 
all  other  magnets  derive  their  power  and  properties 
from  its  effects.  That  the  earth  is  a  magnet,  admits  of 
strong  collateral  proofs.  It  may  be  inferred  from  the 
vast  quantities  of  ferruginous  bodies  contained  in  it, 
which  are  often  dug  up  in  a  magnetic  state,  and  from 
the  magnetism  which  iron  acquires  by  its  position. 
Yet  all  this  carries  us  but  a  very  little  distance  towards 
a  complete  theory  of  magnetism  ;  and  the  difficulties  yet 
in  our  way  are  very  serious.  For  example,  it  is  found 
that  the  magnetical  poles  of  the  earth  change  their 
situation,  and  this  singular  circumstance  has  opened  a 
wide  field  for  speculation.  It  has  been  supposed  that 
the  earth  contains  a  detached  internal  magnet,  which 
has  a  motion  different  from  that  of  the  earth,  though 
their  axes  coincide.  This  internal  loadstone  is  sup- 
posed to  be  separated  from  the  outer  globe,  or  earth,  by 
a  fluid  medium  -f  and,  to  explain  the  constant  variation 
of  the  needle  westward,  the  advocates  of  this  theory 
assume  that  its  motion  with  respect  to  the  earth  is  such, 
that  its  north  pole  revolves  from  east  to  west  at  the 
rate  of  one  degree  in  five  years,  so  as  to  make  a  com- 


MAGNETISM.  191 

plete  revolution  in  1920  years.  To  explain  the  reason 
why  the  motion  of  the  internal  loadstone  should  be 
less  than  that  of  the  earth,  they  suppose  that  the  diur- 
nal motion  of  the  earth  arose  from  an  external  impulse, 
which  was  thence  communicated,  with  a  slight  diminu- 
tion, internally. 

But  this  theory  has  never  given  much  satisfaction. 
The  regularity  of  motion  assigned  to  the  internal  load- 
stone leaves  entirely  unexplained  the  frequent  varia- 
tions actually  observed  ;  and  the  attempt  that  has  been 
made  to  supply  this  deficiency  by  supposing  that  there 
are  within  the  earth  four  magnetic  poles,  which  are 
movable  with  respect  to  each  other,  only  looks  like  a 
wild  effort  to  secure  a  solution  of  the  mystery,  what- 
ever may  be  sacrificed  to  obtain  it.  It  seems  much 
more  rational  to  conclude  that  the  magnetism  of  the 
earth  arises  from  the  magnetism  of  all  the  magnetic 
substances  which  it  contains,  whether  intermixed  with 
other  bodies  or  not ;  that  the  magnetic  poles  of  the 
earth  may  be  considered  as  the  centres  of  the  polarities 
of  all  the  particular  aggregates  of  the  magnetic  sub- 
stances; and  that  these  principal  poles  must  change 
their  places,  relatively  to  the  surface  of  the  earth,  ac- 
cording as  the  particular  aggregations  of  magnetic  sub- 
stances within  the  earth  are,  by  various  causes,  altered 
so  as  to  have  their  power  diminished,  increased,  and 
moved  to  or  from  the  principal  poles.  The  agents 
adequate  to  the  production  of  these  effects  may  be  heat 
and  cold,  volcanoes,  earthquakes,  electricity,  chemical 
decomposition,  and  probably  several  others  of  which 
we  have  no  knowledge. 


ELECTRO-MAGNETISM. 


The  Electro-Magnetic  Telegraph. 

THIS  science  is  of  very  recent  date,  and  must  be 
considered  as  yet  in  its  infancy.  It  was  for  many 
years  suspected  that  there  existed  a  strong  analogy,  if 
not  a  complete  identity,  between  the  electric  and  mag- 
netic fluids ;  and  various  attempts  were  made  to  es- 
tablish such  a  relation  on  satisfactory  principles.  It 
was  known,  for  instance,  that  lightning  destroyed  and 


ELECTRO-MAGNETISM. 


193 


reversed  the  polarity  of  magnetized  needles,  and  that 
it  produced  a  magnetic  power  in  pieces  of  steel.  Now, 
lightning  and  electricity  have  long  been  known  to  be 
the-  same  ;  consequently,  electricity  ought  to  produce 
similar  effects  to  lightning  on  magnetic  and  simple  steel 
bars ;  but  the  attempts  which  were  made  to  discover  a 
satisfactory  proof  of  this  action,  by  means  of  the  electric 
apparatus,  had  little  success ;  and  all  that  was  effected 
in  this  way  amounted  only  to  communicating  the  mag- 
netic property  to  steel  bars,  but  without  enabling  the  ex- 
perimenter to  predict  in  what  directions  the  poles  would 
lie,  —  and  therefore  was  little  more  than  might  be  pro- 
duced by  a  blow,  by  twisting,  and  various  other  means. 
This  method  of  tracing  the  analogy  between  the 
electric  and  magnetic  fluids  having  failed,  recourse 
was  had  to  the  galvanic  battery,  which  was  known  to 
possess  electrical  properties.  By  means  of  this  agent, 
gold  needles  were  magnetized  ;  but  the  relation  be- 
tween the  two  fluids  still  remained  doubtful  till  Pro- 
fessor Oersted,  of  Copenhagen,  instituted  a  series  of 
experiments  which  led  to  the  most  successful  results. 
These  experiments  are  of  too  complicated  a  nature  to 
admit  of  a  detailed  description  here.  The  theory  of 
electro-magnetism  has  not  yet  been  settled,  and  we 
cannot  make  the  principle  of  this  science  intelligible  to 
the  reader  any  further  than  by  saying  that  electric 
currents  are  supposed  to  be  revolving  round  the  com- 
ponent particles  of  magnetized  substances.  When  a 
magnetic  needle  is  placed  near  a  conducting  wire  in 
the  plane  of  the  magnetic  meridian,  and  the  wire  is 
connected  with  a  strong  galvanic  battery,  the  middle 
•will  turn  round,  placing  itself  at  right  angles  to  the 

M          XIII. — 17 


194  ELECTRO-MAGNETISM. 

direction  of  the  current.  Now,  as  the  transmission  of 
electricity  through  a  conducting  substance  is  instanta- 
neous, a  wire  or  other  conductor  may  have  motion 
communicated  to  its  whole  length  at  the  same  moment, 
whatever  that  length  may  be ;  and  it  is  stated  that  an 
electro-magnetic  impulse  may  be  transmitted  at  the 
rate  of  180,000  miles  in  a  second. 

By  the  help  of  this  power  has  been  constructed  that 
wonderful  machine,  the  Electro-magnetic  Telegraph, 
of  which  the  most  successful  and  striking  example  is 
that  of  Professor  Morse.  This  telegraph  extends  from 
Washington  to  Baltimore,  a  distance  of  upwards  of  forty 
miles.  It  consists  of  a  conductor  of  copper  wire,  ex- 
tending, the  whole  distance  between  the  two  cities,  on 
the  tops  of  posts  25  feet  in  height,  and  at  regular  dis- 
tances of  225  feet.  A  galvanic  battery  at  one  end 
transmits  an  electro-magnetic  shock  instantaneously 
through  the  whole  length  of  this  conductor ;  and,  by 
peculiar  management  in  varying  the  shocks,  the  ex- 
tremity of  the  conductor  is  made  to  mark  dots  and 
lines  upon  paper,  by  the  combination  of  which,  the 
letters  of  the  alphabet,  and  figures,  are  signified.  In 
this  manner,  questions  are  asked  and  answered  in  a 
moment  between  the  two  cities.  By  this  wonderful 
machine,  both  space  and  time  are  annihilated,  for  it  is 
obvious  that  no  limit  can  be  assigned  to  the  extent  of 
such  a  correspondence.  The  utility  of  this  invention 
is  obvious  at  first  sight ;  a  system  of  telegraphic  com- 
munication is  already  in  progress  in  the  American 
Union.  Thus  the  transmission  of  news  will  outstrip 
the  sun  in  his  march,  and  the  people  of  St.  Louis  will 
read  at  noon  a  speech  made  at  Washington  at  four  in 
the  afternoon  ! 


MATHEMATICS. 


MATHEMATICS  constitute  the  science  which  has  for 
its  object  the  abstract  relations  of  number  and  magni- 
tude, and  their  application,  through  the  medium  of  ob- 
served laws,  to  the  useful  purposes  of  life  and  the 
explanation  of  natural  phenomena.  From  this  de- 
scription, it  follows  that  mathematical  science  naturally 
divides  itself  into  two  principal  branches.  The  one, 
resting  solely  on  our  intuitive  perceptions  of  abstract 
truth,  and  demanding  no  assistance  from  experience 
and  observation,  and  very  little  from  the  evidence  of 
our  senses,  constitutes  the  pure  mathematics,  and  com- 
prehends all  inquiries  into  the  relations  of  magnitude 
in  the  abstract,  and  the  properties  of  extension.  The 
other,  taking  for  granted  the  truth  of  general  laws  de- 
duced by  legitimate  inference  from  observations  suffi- 
ciently numerous,  supplies  the  hidden  links  which  con- 
nect the  cause  with  its  remote  effect,  and  endeavors, 
from  the  extent  of  the  one,  to  estimate  the  mag- 
nitude of  the  other.  This  branch  is  called  mixed 
mathematics. 

The  science  of  pure  mathematics  enjoys  the  highest 
rank  in  human  knowledge,  its  object  lying  among  the 
most  simple,  the  most  distinct,  and  the  best-defined  of 
our  notions,  while  its  reasoning  consists  of  successive 


196  MATHEMATICS. 

decisions  of  judgment,  in  each  of  which  the  objects  to 
be  compared  are  brought  before  the  mind  with  such 
perfect  clearness  as  to  render  mistake  impossible. 
Analogy,  or  likeness,  that  grand  source  of  human 
error,  is  excluded  from  a  science  in  which  absolute 
equality  or  inequality  in  respect  of  magnitude  is  the 
only  point  which  ever  comes  in  question  ;  while  the 
practice  of  mathematicians,  in  defining  strictly  every 
term,  and  adhering  rigorously  to  their  definition  in  its 
employment,  cuts  off  every  possibility  of  mistake,  from 
inaccuracy  of  language  ;  and  their  extreme  caution  in 
dwelling  upon,  and  analyzing,  each  successive  step  of 
their  reasoning,  saves  them  from  the  danger  of  precip- 
itancy. Mixed  mathematics,  on  the  contrary,  partici- 
pates in  the  uncertainty  which  must  always  attend 
upon  whatever  concerns  human  observation,  however 
far  it  may  be  pushed  —  since  every  conclusion  which 
rests  ultimately  on  such  a  basis  must  be  infected  with 
all  the  errors  to  which  human  observations,  however 
carefully  made,  and  however  often  repeated,  are  liable. 
The  nature  of  this  science  may  be  illustrated  by 
specifying  the  difference  between  a  mathematical  as- 
sertion, and  an  assertion  of  any  other  kind.  If  we  say 
that  two  straight  lines  cannot  completely  enclose  a 
space,  we  utter  a  mathematical  assertion,  which  is  ab- 
stractedly true,  and  the  contrary  to  which  would  be  an 
impossibility.  If  we  say  that  an  unsupported  stone  will 
fall  to  the  ground,  we  state  a  fact,  of  which  we  are  as 
certain,  as  far  as  we  actually  rely  upon  it,  as  of  the 
mathematical  assertion.  But  in  the  mathematical  prop- 
osition, the  idea  of  a  contradiction  to  it  is  an  absurdity 
which  the  mind  instantly  rejects  ;  whereas,  in  the  case 


MATHEMATICS.  197 

of  the  fall  ot  the  stone,  whatever,  the  fact  may  be, 
there  is  no  difficulty  in  conceiving  of  an  exception,  or 
even  of  a  permanent  alteration  of  the  law  by  which  it 
is  made  to  fall. 

Mathematics  may  be  considered  either  as  an  instru- 
ment to  discipline  the  mind,  or  to  assist  us  in  the  inves- 
tigation of  nature  and  the  advancement  of  the  arts. 
In  the  former  point  of  view,  their  object  is  to  strengthen 
the  power  of  logical  deduction  by  frequent  examples ; 
to  give  a  view  of  the  difference  between  reasoning  on 
probable  premises  and  on  certain  ones,  by  the  con- 
struction of  a  body  of  results  which  hi  no  case  in- 
volve any  of  the  uncertainty  arising  from  the  previous 
introduction  of  that  which  may  be  false ;  to  form  the 
habit  of  applying  the  attention  closely  to  difficulties 
which  can  be  conquered  only  by  thought,  and  over 
which  the  victory  is  certain  if  the  right  means  be  used ; 
to  give  caution  in  receiving  that  which,  at  first  sight, 
appears  good  reasoning ;  and  to  instil  a  correct  esti- 
mate of  the  powers  of  the  mind,  by  pointing  out  the 
enormous  extent  of  the  consequences  which  may  be 
developed  out  of  a  few  of  its  most  inherent  notions, 
and  its  utter  incapacity  to  imagine  the  boundaries  of 
knowledge. 

As  instruments  in  the  investigation  of  nature  and 
the  advancement  of  the  arts,  it  is  the  object  of  the 
mathematical  sciences  to  give  correct  habits  of  judg- 
ment, and  ready  means  of  expression,  hi  matters  in- 
volving degree  and  magnitude  of  all  kinds ;  to  teach  the 
method  of  combining  phenomena,  and  ascending  from 
complicated  forms  of  manifestation  to  the  simple  law 
which  regulates  them ;  to  trace  the  necessary  conse- 
17* 


198  MATHEMATICS. 

quences  of  any  law  assumed  on  suspicion,  in  order  to 
compare  those  consequences  with  actual  phenomena ; 
to  make  all  those  investigations  which  are  necessary 
for  the  calculation  of  results,  to  be  used  in  practice  — 
as  in  nautical  astronomy,  application  of  force  and  ma- 
chinery, and  the  conduct  of  money  transactions ;  —  in  a 
word,  to  find  out  truth  in  every  matter  in  which  nature 
is  to  be  investigated,  or  her  powers,  and  those  of  the 
human  mind,  are  to  be  applied  to  the  physical  progress 
of  the  human  race. 

The  mixed  mathematics  are  primarily  dependent  on 
the  extent  and  accuracy  of  our  scrutiny  into  nature  ;  after 
which,  their  further  advancement  is  limited  only  by  the 
degree  of  perfection  to  which  the  pure  mathematics  are 
carried  ;  but  a  very  perfect  knowledge  of  the  latter  is 
requisite  to  a  very  moderate  knowledge  of  the  former. 
The  laws  of  nature,  indeed,  are,  for  the  most  part, 
simple  in  themselves ;  but  the  circumstances  under 
which  they  act  produce  a  complication  in  their 
agencies  which  calls,  at  once,  for  the  most  powerful 
exertions  of  natural  reason,  and  the  most  refined  arti- 
fices of  practised  ingenuity,  to  develop.  Combinations 
are  perpetually  presenting  themselves,  where  the  prin- 
ciples are  satisfactorily  known,  the  general  laws  placed 
beyond  a  doubt,  the  mode  of  applying  mathematical 
investigation  thoroughly  understood — yet  which,  by  the 
mere  complication  of  the  pure  mathematical  inquiries 
which  they  involve,  defy  the  utmost  powers  of  calcu- 
lation. The  restless  activity  of  nature  surrounds  us 
with  minute  phenomena  of  this  kind.  The  motions 
and  equilibrium  of  fluids,  their  capillary  attraction,  the 
vibrations  of  the  atmosphere  and  of  solid  bodies, — every 


MATHEMATICS.  199 

breath  of  wind  that  blows,  and  every  mote  that  sparkles 
in  the  sunbeam,  —  supply  us  with  instances  in  point- 
On  a  wider  scale,  the  simple  law  of  gravitation,  modi- 
fied by  the  consideration  of  three  gravitating  bodies  in 
motion,  produces  a  problem  which  has  resisted  every 
effort  of  ingenuity  and  industry,  stimulated  by  the 
strongest  motives  which  can  rouse  man  to  exertion. 

That  part  of  mathematics  which  treats  of  numbering, 
is  called  arithmetic ;  that  part  which  concerns  measur- 
ing, or  figured  extension,  is  called  geometry  ;  —  these, 
with  algebra  and  fluxions,  which  are  conversant 
with  multitude,  magnitude,  form,  and  motion,  being  the 
foundation  of  all  the  other  parts  of  the  science,  con- 
stitute the  pure  mathematics.  The  science  is  also  dis- 
tinguished into  speculative  and  practical  mathematics ; 
the  former  when  it  is  concerned  in  discovering  proper- 
ties and  relations,  and  the  latter  when  applied  to  prac- 
tice and  real  use  concerning  physical  objects.  The 
peculiar  topics  of  investigation,  in  the  four  principal 
departments  of  pure  mathematics,  may  be  indicated  by 
four  words,  —  namely,  arithmetic  by  number,  geom- 
etry by  form,  algebra  by  generality,  and  fluxions  by 
motion. 

In  mathematics  are  several  general  terms  or  prin- 
ciples, such  as  definitions,  axioms,  &c.,  which  require 
explanation.  A  definition  is  the  explication  of  any 
term  or  word  in  a  science,  showing  the  sense  and 
meaning  in  which  the  term  is  employed  :  every  defini- 
tion ought  to  be  clear,  and  expressed  in  words  that  are 
common  and  well  understood.  A  proposition  is 
something  proposed  to  be  demonstrated,  or  something 
required  to  be  done,  and  is  accordingly  either  a  the' 


200 


MATHEMATICS. 


orem  or  a  problem.  A  theorem  is  a  demonstrative 
proposition,  in  which  some  property  is  asserted,  and 
the  truth  of  it  required  to  be  proved  :  thus  when  it  is 
said  that  the  sum  of  the  three  angles  of  a  triangle  is 
equal  to  two  right  angles,  that  is  a  theorem,  the  truth 
of  which  is  demonstrated  by  geometry.  A  set,  or  col- 
lection, of  such  theorems,  constitutes  a  theory.  A 
problem  is  a  proposition  or  a  question  requiring  some- 
thing to  be  done,  either  to  investigate  some  truth  or  prop- 
erty, or  to  perform  some  operation.  A  limited  problem 
is  that  which  has  but  one  answer ;  an  unlimited  prob- 
lem is  that  which  has  innumerable  answers.  A  de- 
terminate problem  is  that  which  has  a  certain  number 
of  answers.  Solution  of  a  problem  is  the  resolution, 
or  answer  given  to  it.  A  numeral  or  numerical  solu- 
tion is  the  answer,  given  in  numbers  ;  a  geometrical  so- 
lution is  the  answer  given  by  the  principles  of  geome- 
try ;  and  a  mechanical  solution  is  one  which  is  gained 
by  trials  and  experiments. 

A  lemma  is  a  preparatory  proposition,  laid  down  in 
order  to  shorten  the  demonstration  of  the  main  propo- 
sition which  follows  it.  A  corollary,  or  consectary,  is 
a  consequence  drawn  immediately  from  some  propo- 
sition or  principle  previously  demonstrated.  A 
scholium  is  a  remark  or  observation  made  upon  some 
foregoing  proposition  or  premises.  An  axiom,  or 
maxim,  is  a  self-evident  proposition,  requiring  no  formal 
demonstration  to  prove  its  truth,  but  received  and  as- 
sented to  as  soon  as  mentioned  ;  such  as,  The  whole  of 
any  thing  is  greater  than  a  part  of  it ;  or,  The  whole  is 
equal  to  all  its  parts  taken  together,  &c.  A  postulate, 
or  petition,  is  something  required  to  be  done,  which  is 


MATHEMATICS.  201 

so  easy  and  evident  that  no  person  will  hesitate  to 
allow  it.  An  hypothesis  is  a  supposition  assumed  to 
be  true,  in  order  to  argue  from,  or  to  found  upon  it 
the  reasoning  and  demonstration  of  some  proposition. 
Demonstration  is  the  collecting  the  several  arguments 
and  proofs,  and  laying  them  together  in  proper  order,  to 
show  the  truth  of  the  proposition  under  consideration. 
A  direct,  positive,  or  affirmative  demonstration  is  that 
which  concludes  with  the  direct  and  certain  proof  of  the 
proposition  in  hand.  An  indirect  or  negative  demon- 
stration is  that  which  shows  a  proposition  to  be  true  by 
proving  that  some  absurdity  would  necessarily  follow 
if  the  proposition  were  false.  This  is  also  sometimes 
called  reductio  ad  dbsurdum,  because  it  shows  the 
absurdity  and  falsehood  of  all  suppositions  contrary  to 
that  contained  in  the  proposition. 

Method  is  the  art  of  disposing  a  train  of  arguments 
in  a  proper  order  to  investigate  either  the  truth  or  fal- 
sity of  a  proposition,  or  to  demonstrate  it  to  others 
when  it  has  been  found  out.  This  is  either  analytical 
or  synthetical.  Analysis,  or  the  analytic  method, 
is  the  art  or  mode  of  finding  out  the  truth  of  a  proposi- 
tion by  first  supposing  the  thing  to  be  done,  and  then 
reasoning  back,  step  by  step,  till  we  arrive  at  some 
known  truth.  This  is  also  called  the  method  of  in- 
vention, or  resolution.  Synthesis,  or  the  synthetic 
method,  is  the  searching  out  truth  by  first  laying  down 
some  simple  and  easy  principles,  and  then  pursuing 
the  consequences  flowing  from  them,  till  we  arrive  at 
the  conclusion.  This  is  also  called  the  method  of 
composition,  and  is  the  reverse  of  the  analytic 
method,  as  it  proceeds  from  known  principles  to  an 


<t\r&  MATHEMATICS. 

unknown  conclusion,  while  the  other  goes  in  a  retro- 
grade order,  from  the  thing  sought,  considered  as  if  it 
were  true,  to  some  known  principle  or  fact.  There- 
fore, when  any  truth  has  been  found  out  by  the  ana- 
lytic method,  it  may  be  demonstrated  by  a  process  in 
the  contrary  order,  or  by  synthesis. 

The  reader  will  require  no  general  description  of  a 
science  so  well  known  as  ARITHMETIC.  But  there  is 
a  department  of  it  not  very  generally  understood,  — 
namely,  logarithms,  —  the  invention  of  which,  like  many 
other  inventions,  was  the  offspring  of  necessity.  In  the 
infancy  of  astronomy,  before  the  use  of  accurate  instru- 
ments, or  the  discovery  of  the  refined  mathematical 
theories  to  which  they  have  led,  the  calculations  were 
fewer  and  shorter  than  in  modern  times.  As  the 
science  advanced,  however,  they  became  more  labo- 
rious and  irksome,  so  as  to  render  some  method  of 
abridging  them  highly  desirable.  About  the  end  of 
the  sixteenth  century,  some  ingenious  contrivances 
were  found,  by  which  the  labor  of  calculation  might, 
in  particular  cases,  be  shortened.  But  the  most  effec- 
tual, and,  indeed,  the  only  adequate,  remedy  was  the 
artifice  of  logarithms,  which,  from  its  great  utility,  has 
formed  an  epoch  in  the  history  of  science.  This  ad- 
mirable invention  is  due  to  John  Napier,  Baron  of 
Merchiston,  in  Scotland. 

The  word  logarithms  signifies  the  ratio  of  numbers. 
Logarithms,  in  fact,  are  the  numerical  exponents  of 
ratio,  or  a  series  of  numbers  in  arithmetical  progres- 
sions, as  0,  1,  2,  3,  4,  answering  to  another  series  in 
geometrical  progression,  or  as  1,  2,  4,  8,  16,  &c. 
They  facilitate  troublesome  calculations,  in  performing 


MATHEMATICS.  203 

multiplication  by  simple  addition ;  and  performing 
division  by  subtraction ;  and  raising  of  powers  in  multi- 
plying the  logarithm  by  the  index  of  the  power ;  and 
extracting  of  roots  in  dividing  the  logarithm  of  the 
number  by  the  index  of  the  root ;  for  logarithms  are 
numbers  so  contrived  and  adapted  to  other  numbers, 
that  the  sums  and  differences  of  the  former  shall 
correspond  to,  and  show,  the  products  and  quotients  of 
the  latter. 

ALGEBRA  is  the  science  of  investigation  by  means  of 
symbols.  It  is  sometimes  also  called  analysis,  and  is 
a  general  kind  of  arithmetic,  or  universal  way  of  com- 
putation. In  this  science,  quantities  of  all  kinds  are 
represented  by  the  letters  of  the  alphabet;  and  the 
operations  to  be  performed  by  them — as  addition,  sub- 
traction, &c.  — are  denoted  by  certain  simple  characters, 
instead  of  being  expressed  in  words  at  length.  These 
characters,  unlike  the  numerals  of  arithmetic,  being 
altogether  arbitrary,  are  employed  to  denote  not  only 
known  quantities,  but  also  the  quantities  which  are 
required,  or  unknown.  In  some  cases,  the  known  quan- 
tities are  most  conveniently  expressed  by  the  common 
numeral  characters,  as  in  arithmetic ;  but  in  others  it 
is  better  to  represent  both  the  known  and  the  unknown 
quantities  by  other  symbols.  The  letters  of  the  alphabet 
being  usually  selected  for  this  purpose,  it  is  common 
to  employ  those  at  the  beginning,  as  a,  J,  c,  rf,  &c.,  for 
known  quantities,  and  those  at  the  end,  as,  z,  y,  a,  &c., 
for  the  unknown.  There  are  also  certain  arbitrary 
signs  used  to  express  the  relations  of  quantities  to  one 
another,  and  the  operations  which  may  be  performed 
on  them. 


204  MATHEMATICS. 

GEOMETRY  is  the  science  or  doctrine  of  local  exten- 
sion —  as  of  lines,  surfaces,  and  solids,  with  that  of 
ratios,  &c.  The  word  signifies,  literally,  measuring  of 
the  earth,  as  it  was  the  necessity  of  measuring  land 
which  first  gave  occasion  to  study  the  principles  and 
rules  of  this  art,  which  has  since  been  extended  to 
numberless  other  speculations, —  so  that,  together  with 
arithmetic,  geometry  now  constitutes  the  chief  founda- 
tion of  mathematical  science :  it  is  distinguished  into 
theoretical,  or  speculative,  and  practical.  Theoretical 
or  speculative  geometry  treats  of  the  various  proper- 
ties and  relations  in  magnitudes,  demonstrating  the- 
orems, &c.  Practical  geometry  is  that  which  applies 
those  speculations  and  theorems  to  particular  uses  in  the 
solution  of  problems,  and  in  measurements  in  the  ordi- 
nary concerns  of  life.  Speculative  geometry,  again, 
may  be  divided  into  elementary  and  sublime.  Ele- 
mentary or  common  geometry  is  that  which  is  em- 
ployed in  the  consideration  of  right  lines  and  plane 
surfaces,  with  the  solids  generated  from  them.  Higher 
or  sublime  geometry  is  employed  in  the  consideration 
of  curve  lines,  conic  sections,  and  the  bodies  formed 
from  them.  This  part  has  been  chiefly  cultivated  by 
the  moderns,  by  help  of  the  improved  state  of  algebra, 
and  the  modern  analysis,  or  fluxions.  In  the  doctrine 
of  fluxions,  magnitudes  or  quantities  of  all  kinds  are 
considered  as  not  made  up  of  a  number  of  small  parts, 
but  as  generated  by  continued  motion,  by  means  of 
which  they  increase  or  decrease  ;  as  a  line  by  the  mo- 
tion of  a  point ;  a  surface  by  the  motion  of  a  line  ;  and 
a  solid  by  the  motion  of  a  surface.  So,  likewise,  time 
may  be  considered  as  represented  by  a  line,  increasing 


205 

uniformly  by  the  motion  of  a  point ;  and  quantities  of 
all  kinds  whatever,  which  are  capable  of  increase  or 
decrease,  may,  in  like  manner,  be  represented  by  lines, 
surfaces,  or  solids,  considered  as  generated  by  motion. 
Any  quantity  thus  generated  and  variable  is  called  a 
fluent,  or  a  flowing  quantity  ;  and  the  rate  or  propor- 
tion according  to  which  any  flowing  quantity  increases, 
at  any  position  or  instant,  is  the  fluxion  of  the  said 
quantity  at  that  position  or  instant. 

TRIGONOMETRY,  in  its  original  sense,  signified  that 
part  of  mathematical  science  which  treated  of  the  ad- 
measurement of  triangles.  These  triangles  were  sup- 
posed to  be  described  either  upon  a  plane  or  upon  the 
surface  of  a  sphere  ;  and  hence  the  science  was  divided 
into  plane  trigonometry  and  spherical  trigonometry. 
Like  every  other  department  of  science,  the  objects  of 
trigonometry  became  more  extended  as  knowledge  ad- 
vanced and  discovery  accumulated  ;  and  this  part  of 
mathematics,  which  was  at  first  confined  to  the  solution 
of  one  general  problem,  —  namely,  certain  sides  and 
angles  of  a  triangle  being  known,  how  to  determine  the 
others,  —  has  now  spread  its  uses  over  the  whole 
domain  of  mathematical  and  physical  science.  In  the 
wide  range  of  modern  analysis,  there  is  scarcely  a  sub- 
ject of  investigation  to  which  trigonometry  has  not 
imparted  clearness  and  perspicuity,  by  the  use  of  its 
language  and  its  principles.  The  immediate  object  of 
this  science  is  to  institute  a  system  of  symbols,  and  to 
establish  principles  by  which  angular  magnitude  may 
be  submitted  to  computation,  and  numerically  con- 
nected with  other  species  of  magnitude  ;  so  that  angles, 
and.  the  quantities  on  which  they  depend,  or  which 
xm.— 18 


206  MATHEMATICS. 

depend  on  them,  may  have  their  mutual  relations  in- 
vestigated by  the  same  methods  of  computation  that 
are  applied  to  all  other  quantities. 

Every  triangle  has  six  parts,  —  namely,  three  angles 
and  three  sides,  and  it  is  necessary  that  three  of  these 
parts  be  given,  to  find  the  other  three.  In  spherical 
trigonometry,  the  three  parts  that  are  given  may  be  of 
any  kind  —  either  all  sides,  or  all  angles,  or  part  the 
one  and  part  the  other.  But  in  plane  trigonometry,  it  is 
necessary  that  one  of  the  three  parts,  at  least,  be  a  side, 
since  from  three  angles  can  only  be  found  the  propor- 
tions of  the  sides,  but  not  the  real  quantities  of  them. 
Trigonometry  is  of  the  greatest  use  in  the  mathe- 
matical sciences,  especially  in  astronomy,  navigation, 
surveying,  dialling,  geography,  &c.  By  help  of  it  we 
ascertain  the  magnitude  of  the  earth  and  the  stars, 
their  distances,  motions,  eclipses,  &c. 

The  usefulness  of  the  mathematical  sciences  may  be 
illustrated  by  an  example.  Numberless  experiments 
have  shown  us  that  all  bodies  near  the  earth's  surface 
fall  with  an  accelerated  velocity,  and  that  the  spaces 
passed  through  are  as  the  squares  of  the  times  they 
have  been  in  falling.  This,  then,  the  mathematician 
considers  as  a  necessary  and  essential  quality  of  mat- 
ter ;  and  with  this  datum  he  proceeds  to  examine  what 
will  be  the  velocity  of  a  body  after  any  given  time ; 
in  what  manner  it  will  have  acquired  any  given  ve- 
locity ;  what  time  is  necessary  for  it  to  have  generated 
a  given  space,  &c.  In  all  these  investigations,  his  con- 
clusions are  as  certain  and  indisputable  as  any  of  those 
which  geometry  deduces  from  self-evident  truths  and 
definitions.  Again  in  optics,  —  having  established  it  as 


MATHEMATICS.  207 

a  principle  of  light,  that  it  is  transmitted  in  right  lines 
while  no  obstacle  is  opposed  to  the  passage  of  the  rays ; 
that  it  is  reflected  and  refracted  in  a  particular  man- 
ner, —  he  considers  the  rays  only  as  right  lines,  the 
surfaces  of  the  bodies  which  cause  their  reflection  and 
refraction  only  as  geometrical  planes,  the  form  of 
which  alone  enters  into  his  investigation ;  and  from  this 
point,  all  his  inquiries  are  purely  geometrical ;  his  in- 
vestigation  is  clear  and  perspicuous,  and  his  deduction 
evident  and  satisfactory.  To  this  class  of  mathematics 
belong  mechanics,  or  the  science  of  equilibrium; 
hydro-dynamics,  in  which  the  equilibrium  and  motion 
of  fluids  are  considered ;  astronomy,  which  relates  to 
the  motion,  masses,  distances,  and  densities  of  the 
heavenly  bodies ;  optics,  or  the  theory  and  effects  of 
light ;  and  acoustics,  or  theory  of  sounds. 

Such  are  the  subjects  that  fall  under  the  contempla- 
tion of  the  mathematician  ;  and,  as  far  as  a  knowledge 
of  these  may  be  considered  beneficial  to  mankind,  so  far, 
at  least,  the  utility  of  the  science  on  which  they  depend 
must  be  admitted.  It  is  not,  however,  the  application 
of  mathematics  to  subjects  connected  with  common 
life,  that  constitutes  their  peculiar  excellence  ;  it  is 
their  operation  on  the  mind,  the  vigor  they  impart  to 
our  intellectual  faculties,  and  the  discipline  which  they 
impose  upon  our  wandering  reason.  "  The  mathe- 
matics," says  Dr.  Barrow,  "effectually  exercise,  not 
vainly  delude,  nor  vexatiously  torment,  studious  minds 
with  obscure  subtilties ;  but  plainly  demonstrate  every 
thing  within  their  reach,  draw  certain  conclusions,  in- 
struct by  profitable  rules,  and  unfold  pleasant  questions. 
These  disciplines  also  inure  and  corroborate  the  mind 


208  MATHEMATICS. 

to  a  constant  diligence  in  study ;  they  wholly  deliver  us 
from  a  credulous  simplicity,  and  most  strongly  fortify 
us  against  the  vanity  of  skepticism ;  they  effectually 
restrain  us  from  a  rash  presumption,  and  easily  incline 
us  to  a  due  assent,  and  perfectly  subject  us  to  the  gov- 
ernment of  right  reason.  While  the  mind  is  abstracted 
and  elevated  from  sensible  matter,  it  distinctly  views 
pure  forms,  conceives  the  beauty  of  ideas,  and  inves- 
tigates the  harmony  of  proportions ;  the  manners 
themselves  are  sensibly  corrected  and  improved ;  the 
affections  composed  and  rectified;  the  fancy  calmed 
and  settled ;  and  the  understanding  raised  and  excited 
to  more  divine  contemplations." 

Many  will  consider  the  above  as  the  language  of  an 
enthusiast,  for  the  science  of  mathematics  is  not  with- 
out its  detractors.  It  has  been  represented  as  a  science 
which  blunts  all  the  tender  feelings  of  our  nature,  and 
renders  those  who  cultivate  it  vain,  arrogant,  and  pre- 
sumptuous ;  as  destroying  all  relish  for  works  of  taste 
and  imagination,  hardening  the  heart  against  every 
truth  but  those  of  the  demonstrative  kind,  and,  conse- 
quently, as  having  a  tendency  to  lead  men  to  infidelity 
and  atheism.  Dr.  Johnson  seems  to  have  been  tinc- 
tured with  these  opinions.  "It  was  the  great  praise 
of  Socrates,"  he  observes,  "  that  he  drew  the  wits  of 
Greece,  by  his  instruction  and  example,  from  the  vain 
pursuits  of  natural  philosophy  to  moral  inquiries ;  and 
turned  their  thoughts,  from  stars  and  tides,  and  matter 
and  motion,  to  the  various  modifications  of  virtue  and 
the  relations  of  life."  He  pursues  this  thought  still 
further,  and  illustrates  it  by  a  story  which  he  tells  of 
one  Gelidus,  a  mathematician,  who  was  so  absorbed  in 


MATHEMATICS.  209 

I 

his  speculations,  that,  when  his  servants  came  to  ac- 
quaint him  that  a  house  was  on  fire,  and  the  whole 
neighborhood  in  danger  of  being  burnt,  he  only  replied, 
"  that  it  was  very  likely,  for  it  was  the  nature  of  fire  to 
act  in  a  circle."  He  even  divests  this  philosopher  of 
the  common  feelings  of  humanity,  and  makes  him  as 
insensible  to  the  wants  of  his  family  as  to  the  dis- 
tresses of  his  neighbors.  This,  however,  is  but  a 
specimen  of  Johnson's  illiberal  feelings  towards  the 
professors  of  a  science  for  which  he  happened  to  pos- 
sess no  taste.  A  great  and  comprehensive  genius  ex- 
cludes none  of  the  sciences ;  they  all  contribute,  by 
various  means,  to  adorn  and  improve  human  life, 
and  consequently  are  all  deserving  of  esteem  and 
patronage. 

N  18* 


METEOROLOGY 


METEOROLOGY  may  be  defined  as  that  department 
of  physical  science  which  treats  of  atmospherical  phe- 
nomena. The  word  meteor  has,  in  our  language, 
been  almost  exclusively  confined  to  those  luminous 
bodies  which  are  seen  occasionally  in  the  atmosphere, 
and  whose  appearance  and  motion  have  not  yet  been 
reduced  to  any  definite  law.-  In  Greek,  however,  the 
word  meteora  was  indiscriminately  applied  to  all  bodies, 
whether  luminous  or  opaque,  that  appeared  in  the  at- 
mosphere ;  and  the  term  meteorology  is  still  used  in  the 
same,  and  even  a  more  extended,  signification.  It  de- 
notes the  investigation,  not  merely  of  those  atmospheri- 


JiETEOHOLOGT.  211 

cal  phenomena  that  are  of  comparatively  rare  occur- 
rence, and  may  be  more  properly  denominated  meteors, 
but  of  the  various  changes,  also,  that  are  observed  to 
take  place  in  the  state  of  the  atmosphere  itself.  But 
for  this  extended  application  of  the  word,  the  subject 
would  be  comparatively  uninteresting,  and  could  with 
little  propriety  be  dignified  with  the  appellation  of  a 
science. 

To  the  first  class  of  atmospherical  phenomena  belong 
those  luminous  bodies  that  occasionally  appear  in  the 
sky,  and  have  been  denominated  meteors,  or  shooting 
stars.  These  bodies  appear  to  be  of  different  magni- 
tudes, and  even  of  various  forms,  though  this  last  cir- 
cumstance may,  perhaps,  be  the  effect  of  optical  de- 
ception. In  general,  they  seem  to  be  globular,  con- 
tinuing visible  only  for  a  few  seconds,  and  moving  with 
great  velocity.  Their  course  is,  on  some  occasions,  in 
a  straight  line,  and  on  others,  curvilinear,  rendered 
more  distinct  by  the  tail,  or  luminous  train,  which  they 
leave  behind  them  ;  and  before  disappearing,  they  are 
sometimes  separated  into  several  smaller  bodies,  accom- 
panied with  an  explosion  resembling  thunder,  more  or 
less  loud  in  proportion  to  their  magnitude  and  distance. 
These  explosions  are  followed  sometimes  by  a  shower 
of  solid  bodies,  of  a  stony  or  metallic  substance,  some 
of  which  appear  luminous  in  their  descent  after  the 
explosion,  and  have  been  taken  up  before  they  had 
time  to  cool  We  have  already  alluded  to  the  subject 
of  these  meteorites  in  another  part  of  this  volume. 

Another  meteoric  appearance  is  known  by  the  name 
of  the  ignis  faiuus,  Jack-icith-a-lantern,  and  TT777- 
with-the-wisp.  It  is  generally  seen  in  dark  nights,  over 


212 


METEOROLOGY. 


boggy  and  marshy  ground,  but  generally  in  motion,  at 
the  height  of  five  or  six  feet,  skipping  from  place  to 
place,  and  frequently  changing,  both  in  magnitude  and 
form.  On  some  occasions,  it  is  observed  to  be  sud- 
denly extinguished,  and  then  to  reappear  at  a  distance 
from  its  former  position.  Those  persons  who  have 
endeavored  to  examine  it  closely  have  found,  that  it 
moves  away  from  them  with  a  velocity  proportioned  to 
that  with  which  they  advance  —  a  circumstance  which 
has  had  no  small  influence  on  the  fears  of  the  ignorant 
and  superstitious.  Dr.  Derham  once  saw  an  ignis 
fatuus  in  a  boggy  place,  between  two  rocky  hills,  in  a 
dark  and  calm  night.  He  approached  by  degrees 
within  two  or  three  yards  of  it,  and  thereby  had  an 
opportunity  of  viewing  it  to  the  best  advantage.  It 
kept  skipping  about  a  dead  thistle,  till  a  slight  motion 
of  the  air — occasioned,  as  he  supposed,  by  his  near 
approach  —  caused  it  to  jump  to  another  place;  and  as 
he  advanced,  it  kept  flying  before  him.  He  observed  it 
to  be  a  uniform  body  of  light,  and  concluded  it  must 
consist  of  ignited  vapor.  These  appearances  are  very 
common  on  the  plains  near  Bologna,  in  Italy,  where 
they  sometimes  flit  before  the  traveller  on  the  road, 
saving  him  the  expense  of  a  torch  on  d'ark  nights. 
Sometimes  they  spread  very  wide,  and  then  contract 
themselves;  and  sometimes  they  float  like  waves,  and 
appear  to  drop  sparks  of  fire.  They  are  more  fre- 
quent, in  that  quarter,  when  the  ground  is  covered  with 
snow  than  in  the  heat  of  summer,  and  shine  more 
strongly  in  rainy  than  in  dry  weather. 

A  meteoric  appearance  of  the  same  kind  is  some- 
*imes   met  with,  at  sea,  during  gales  of  wind,  and, 


METEOROLOGY.  213 

of  course,  has  become  connected  with  many  super- 
stitious notions  of  the  sailors,  who  call  it  a  corpo- 
sant. There  are  sometimes  two  together,  and  these 
are  named  Castor  and  Pollux.  The  following  is  a 
description  of  one  given  by  the  voyager  Dampier : 
"  After  4  o'clock  the  thunder  and  the  rain  abated,  and 
then  we  saw  a  corpusant  at  our  maintopmast  head, 
on  the  very  top  of  the  truck  of  the  spindle.  This  sight 
rejoiced  our  men  exceedingly,  for  the  height  of  the 
storm  is  commonly  over  when  the  corpusant  is  seen 
aloft ;  but  when  they  are  seen  lying  on  the  deck,  it  is 
generally  accounted  a  bad  sign.  A  corpusant.  is  a 
certain  small,  glittering  light ;  when  it  appears,  as  this 
did,  on  the  very  top  of  a  mainmast,  or  at  a  yard-arm, 
it  is  like  a  star ;  but  when  it  appears  on  the  deck,  it 
resembles  a  great  glow-worm.  The  Spaniards  have 
another  name  for  it ;  though  I  take  even  this  to  be  a 
Spanish  or  Portuguese  name,  and  a  corruption  only  of 
corpus  sanctum ;  and  I  have  been  told  that,  when  they 
see  them,  they  presently  go  to  prayers,  and  bless 
themselves  for  the  happy  sight.  I  have  heard  some 
ignorant  seamen  discoursing  how  they  have  seen  them 
creep,  or,  as  they  say,  travel  about,  in  the  scuppers, 
telling  many  dismal  stories  that  happened  at  such 
times ;  but  I  did  never  see  any  one  stir  out  of  the  place 
where  it  was  first  fixed,  except  upon  deck,  where  every 
sea  washeth  it  about.  Neither  did  I  ever  see  any,  but 
when  we  have  had  hard  rain  as  well  as  wind,  and, 
therefore,  do  believe  it  is  some  jelly."  The  origin 
and  nature  of  the  remarkable  lights  above  described 
have  not  yet  been  explained ;  more  numerous  and 
accurate  observations  than  have  been  made  are  re- 


214  METEOROLOGY. 

quired,  to  furnish  the  basis  of  an  accurate  theory 
respecting  them. 

Besides  these  meteors,  there  are  other  luminous  ap- 
pearances occasionally  observed  in  the  atmosphere  — 
namely,  haloes,  parhelia,  or  mock-suns,  and  paraselenai, 
or  mock-moons.  These  are  supposed  to  indicate  cer- 
tain approaching  changes  of  the  weather.  The  lumi- 
nous circle  which  is  sometimes  seen  around  the  heav- 
enly bodies,  but  especially  the  sun  and  moon,  and 
which  has  received  the  name  of  halo,  or  corona,  has, 
from  a  very  early  period,  been  regarded  as  a  certain 
prognostication  of  stormy  weather,  accompanied  with 
rain  or  snow,  according  to  the  climate  or  season.  It 
frequently  happens  that,  in  the  outer  edge  or  circumfer- 
ence of  this  circle,  there  is  a  part  less  distinctly  defined 
than  the  rest,  apparently  owing  to  the  contact  of  a 
denser  cloud  ;  and  it  has  been  remarked  by  shepherds, 
and  others  who  have  frequent  opportunities  of  observ- 
ing this  phenomenon,  that  the  storm  generally  comes 
from  that  point  of  the  compass  towards  which  this  in- 
distinct portion  of  the  circle,  or  opening,  as  it  is  called, 
is  directed.  This  phenomenon,  as  well  as  its  modifica- 
tions, the  parhelion  and  the  paraselene,  is  obviously 
connected  with  a  change  of  weather  only  in  so  far  as  it 
indicates  some  peculiarity  in  the  existing  state  of  the 
atmosphere.  The  same  remark  applies  to  the  rain- 
bow, though  this  last  is  rather  a  concomitant,  than  a 
prognostic,  of  rain.  It  has  been  remarked,  however, 
that  a  rainbow  in  the  morning  is  frequently  followed 
by  showers,  while  one  in  the  evening  forebodes  fair 
weather. 

It  has  long  been  a  received  opinion  that  the  phases 


METEOROLOGY.  ,  215 

of  the  moon  have  a  certain  influence  on  the  weather, 
and  these  have  accordingly  furnished  various  prognos- 
tications. It  is  quite  conceivable,  on  philosophical  prin- 
ciples, that  the  atmosphere  may  be  differently  affected, 
in  the  same  way  as  the  waters  of  the  ocean  are,  by  the 
different  positions  of  the  sun  and  moon  relatively  to 
the  earth ;  and  that  the  result,  in  certain  cases,  may  be 
a  tract  of  settled  or  tempestuous  weather,  according  to 
circumstances.  At  the  same  time,  the  subject  is  still 
involved  in  great  uncertainty,  nor  does  there  appear  to 
be  any  foundation  for  the  popular  opinion  that  certain 
sorts  of  weather  will  follow  the  changing  of  the  moon, 
according  as  it  happens  in  the  east,  west,  south,  &c. 

But  the  most  fertile  source  of  prognostics  is  to  be 
found  in  the  various  and  ever-changing  appearance  of 
the  clouds.  As  the  proximate  cause  of  rain  or  snow, 
they  have  in  all  ages  been  regarded  as  affording  the 
surest  and  most  direct  intimation  of  approaching 
changes  ;  and  there  are  few  persons,  perhaps,  who  are 
not  conscious  of  having  frequently  looked,  instinctivelj 
as  it  were,  to  the  appearance  of  the  clouds,  in  order  to 
form  some  opinion  or  conjecture  respecting  the  future 
state  of  the  weather.  At  the  same  time,  there  are  few 
subjects  on  which  there  exist  so  great  a  diversity  and 
vagueness  of  opinion.  Indications  drawn  from  the 
appearances  of  the  clouds  themselves  are  exceedingly 
indistinct,  unless  when  accompanied  with  other  circum- 
stances, which  render  them  more  definite,  —  such  as  the 
color  of  the  sky  at  sunrise  or  sunset,  the  settling  of 
clouds  on  the  summit  of  hills,  the  appearance  of 
mist  or  fog  at  particular  periods  of  the  moon's  age, 
&c.  And  though  there  are,  no  doubt,  certain  modifi- 


216   l  METEOROLOGY. 

cations  of  the  forms  of  clouds,  which  nine,  perhaps, 
out  of  ten,  among  weather-wise  persons,  would  without 
hesitation  pronounce  to  be  indications  of  rain  or  snow, 
yet,  if  they  were  required  to  assign  a  specific  reason 
for  their  opinion,  scarcely  two  of  them  would  be  found 
to  agree. 

The  following  passage  from  Virgil's  Georgics  will 
show  what  prognostics  of  weather  were  regarded  by 
the  Romans  in  his  day :  — 


Observe  the  daily  circle  of  the  sun, 

And  the  short  year  of  each  revolving  moon ; 

By  them  thou  shalt  foresee  the  following  day, 

Nor  shall  a  starry  night  thy  hopes  betray. 

When  first  the  moon  appears,  if  then  she  shrouds 

Her  silver  crescent,  tipped  with  sable  clouds, 

Conclude  she  bodes  a  tempest  on  the  main, 

And  brews  for  fields  impetuous  floods  of  rain  : 

Or  if  her  face  with  fiery  flushing  glow, 

Expect  the  rattling  winds  aloft  to  blow. 

But,  four  nights  old —  for  that's  the  surest  sign  — 

With  sharpened  horns  if  then  she  glorious  shine, 

Next  day,  nor  only  that,  but  all  the  moon, 

Till  her  revolving  race  be  wholly  run, 

Are  void  of  tempests  both  by  land  and  sea, 

And  sailors  in  the  port  their  promised  vows  shall  pay 

Above  the  rest,  the  sun,  who  never  lies, 

Foretells  the  change  of  weather,  in  the  skies. 

For,  if  he  rise  unwilling  to  his  race, 

Clouds  on  his  brow,  and  spots  upon  his  face, 

Or  if  through  mists  he  shoot  his  sullen  beams, 

Frugal  of  light,  in  loose  and  straggling  streams, 

Suspect  a  drizzling  day,  with  southern  rain,         , 

Fatal  to  fruit,  and  flocks,  and  promised  grain  : 

Or  if  Aurora,  with  half-opened  eyes, 

And  a  pale,  sickly  cheek,  salute  the  skies, 


METEOROLOGY.  217 

How  shall  the  vine,  with  tender  leaves,  defend 

Her  teeming  clusters,  when  the  storms  descend  ? 

When  ridgy  roofs,  and  tiles,  can  scarce  avail 

To  bar  the  ruin  of  the  rattling  hail  ? 

But  more  than  all  the  getting  sun  survey, 

When  down  the  steep  of  heaven  he  drives  the  day. 

For  oft  we  find  him  finishing  his  race, 

With  various  colors  erring  on  his  face. 

If  fiery  red  his  glowing  globe  descends, 

High  winds  and  furious  tempests  he  portends ; 

But  if  his  cheeks  are  swollen  with  livid  blue, 

He  bodes  wet  weather  by  his  watery  hue. 

If  dusky  spots  are  varied  on  his  brow, 

And,  streaked  with  red,  a  troubled  color  show, 

That  sullen  mixture  shall  at  once  declare 

Winds,  rains,  and  storms,  and  elemental  war. 

But  if  with  purple  ray  he  brings  the  light, 

And  a  pure  heaven  resigns  to  quiet  night, 

No  rising  winds  or  falling  storms  are  nigh, 

But  northern  breezes  through  the  forest  fly, 

And  drive  the  rack,  and  purge  the  ruffled  sky. 

Th'  unerring  sun  by  certain  signs  declares 

What  the  late  even  or  early  morn  prepares  ; 

And  when  the  south  projects  a  stormy  day, 

And  when  the  clearing  north  will  puff  the  clouds  away. 


There  is  another  class  of  prognostics — namely,  those 
which  are  derived  from  phenomena  observed  on  the 
surface  of  the  earth,  or,  at  least,  in  the  lower  regions 
of  the  atmosphere.  These  are  of  various  kinds  —  such 
as  the  expansion  and  contraction  of  flowers ;  the  mo- 
tions and  cries  of  certain  animals ;  painful  sensations  in 
the  human  body,  &c. ;  and  though  many  of  these  are 
no  doubt  fanciful,  yet  others  appear  well  entitled  to  the 
attention  of  meteorologists.  Some  of  them,  indeed,  es- 
pecially such  as  are  drawn  from  the  economy  of  plants. 
XIH.— 19 


218  METEOROLOGY. 

admit  of  a  philosophical  and  satisfactory  explanation,  as 
every  one  must  know  who  is  acquainted  with  physiologi- 
cal botany.  It  is  probably  owing  to  some  atmospherical 
influence,  of  a  similar  kind,  on  the  animal  system,  that 
the  peculiar  cries  and  motions  of  some  beasts,  and  cer- 
tain sensations  in  the  human  body,  are  found  to  indi- 
cate changes  in  the  weather ;  though  it  may  be  diffi- 
cult, or,  in  the  present  state  of  science,  even  impossible, 
to  explain  that  influence.  Thus  it  has  been  long  ob 
served,  and  very  generally  believed,  that  rain  may  be 
expected  when  swallows  are  seen  dipping  their  wings 
in  the  water  over  which  they  are  flying;  when  the 
crow  cries  more  than  usual ;  when  water-fowl  are 
more  than  usually  clamorous  and  active ;  when  dogs 
and  cats  are  dull  and  sleepy ;  when  the  croaking 
of  frogs  is  loud  and  general :  when  worms  are  seen 
in  great  numbers  on  the  surface  of  the  earth  ;  when 
pigs  run  up  and  down  with  evident  signs  of  uneasiness, 
which  has  given  rise  to  the  proverbial  saying  about 
"  the  pig  that  sees  the  wind."  In  the  United  States, 
we  have  various  animals  who  announce  changes  of 
weather  by  their  cries.  A  little  reptile  called  the  tree- 
toad,  or  tree-frog,  is  very  clamorous  before  a  shower ; 
and  the  American  quail,  whose  note  sounds  remarkably 
like  the  words  more  wet,  gives  the  same  warning. 

That  a  change  in  the  atmosphere,  not  perceptible  by 
any  appearance  in  the  heavens,  may  yet  affect  the  sen- 
sations of  the  human  body  as  well  as  those  of  animals, 
is  evident  from  the  notorious  fact  that  persons  subject 
to  rheumatism,  and  similar  diseases,  or  who  have  acci- 
dentally suffered  any  injury  in  their  limbs,  generally 
feel  more  acute  pain  in  the  part  affected  before  a 


METEOROLOGY.  219 

change  of  weather  than  at  any  other  time ;  and  there 
are  instances  where  these  pains  are  most  severe  before 
or  during  a  sudden  fall  of  the  barometer.  This  coinci- 
dence points  to  something  like  an  explanation  of  the 
phenomenon ;  but  the  subject  has  not  yet  been  properly 
investigated. 

The  different  parts  of  the  surface  of  the  globe  are 
unequally  exposed  to  the  impression  of  the  solar  rays, 
and  the  intensity  of  this  action  depends  on  the  latitude. of 
the  place,  on  the  changes  which  take  place  during  the 
day  and  the  night,  &c.  Between  this  variable  condition 
of  the  surface,  and  that  of  the  temperature  of  the  atmos- 
phere, some  relation  must  exist,  which  a  well-devised 
theory  must  ultimately  unfold.  The  heat  existing  from 
day  to  day  in  that  portion  of  the  atmosphere  which  is 
next  the  earth,  is  at  no  time  the  simple  product  of  the 
direct  action  of  the  solar  rays  on  that  portion  ;  and  the 
accumulation  of  heat  near  the  surface  is  evidently  due 
to  the  stopping  of  the  rays  at  that  surface,  to  their  mul- 
tiplied reflections  and  refractions,  in  consequence  of 
which  they  are,  as  it  were,  absorbed  and  fixed  for  a 
time  in  the  soil  and  in  the  incumbent  atmosphere. 
By  this  process,  the  earth,  when  in  a  cold  state,  at  the 
end  of  winter,  becomes  gradually  heated  to  a  certain 
depth  as  the  warm  season  advances ;  and  on  the  other 
hand,  as  the  sun  declines  in  autumn,  the  heated  soil 
acts  as  a  warm  body  on  the  atmosphere,  and  gives  out 
again  the  heat  it  had  received,  and,  as  it  were,  stored 
up.  Similar  vicissitudes  during  the  day  and  the  night, 
according  as  the  sun's  action  is  exercised  or  with- 
drawn from  the  terrestrial  surface,  contribute,  in  their 
part,  to  that  unceasing  variety  which  characterizes  all 


220  METEOROLOGY. 

the  conditions  of  the  great  body  of  air  surrounding  it 
It  appears,  from  experiments,  that,  were  the  earth's  sur- 
face at  a  mean  temperature,  and  the  solar  rays  sud- 
denly intercepted,  it  would  require  about  thirty  days  to 
cool  it  down  seven  degrees,  and  about  the  same  time 
to  heat  it  to  its  former  temperature  on  their  return. 

Our  knowledge,  however,  of  the  actual  condition  of 
the  earth's  internal  temperature,  must  be  derived  from 
observations  made  below  its  surface.  It  has  been  as- 
certained that,  at  a  certain  depth  below  the  surface, 
the  temperature  maintains  a  nearly  constant  character 
during  the  circling  changes  of  the  year ;  and  this  per- 
manent temperature  is  lower  according  as  the  place  is 
more  distant  from  the  equator.  We  have  before  re- 
marked, that  the  heat  of  the  earth  increases  as  we 
descend.  The  reverse  of  this  takes  place  in  ascending 
into  the  atmosphere ;  and  on  very  high  mountains  we 
come  to  a  region  of  perpetual  snow,  even  under  the 
equator.  Enormous  beds  of  clouds  hang  upon  these 
mountains  between  the  snowy  region  and  the  plains 
below,  and  increase  the  coldness  of  the  mountain-tops, 
by  interrupting  the  radiation  of  the  caloric  from  the 
Inferior  parts.  That  increases  the  elastic  power  of  the 
air ;  consequently,  the  equilibrium  of  the  atmosphere, 
when  unequally  heated,  must  be  constantly  disturbed ; 
the  currents  of  warm  and  cold  air  change  places, 
—  the  cold  moving  to  the  warm  region,  and  thence, 
when  warmed,  repeating  the  course  of  the  warm  air. 
It  will  not  be  difficult,  from  this,  to  understand  the  cause 
of  the  sudden  and  violent  changes  of  weather  in  very 
mountainous  regions. 

There  is  scarcely  any  subject  in  which  mankind  fee 


METEOROLOGY.  221 

themselves  more  interested  than  in  the  state  of  the 
weather ;  and  it  would  be  an  amusing  undertaking  to 
calculate  how  much  of  our  time  is  passed  in  telling 
one  another  it  is  hot,  it  is  cold,  it  is  fine  weather,  it  is 
a  beautiful  day,  tkc.  We  have  all  been  accustomed  to 
see  clouds  from  our  infancy.  They,  therefore,  neither 
awaken  admiration,  nor,  in  common  cases,  excite 
attention ;  yet,  of  all  the  objects  around  us,  there  are 
few  more  wonderful,  or  more  truly  deserving  of  notice. 
The  traveller  who  has  ascended  high  mountains 
knows  that  clouds  are  a  species  of  fog,  or  mist,  like 
those  which  we  perceive  upon  plains ;  he  has  also  re- 
marked that,  when  the  clouds  are  scattered  in  the  air, 
the  stratum  of  the  atmosphere  in  which  they  float  is 
comparatively  dry.  Clouds  are  composed  of  a  mass 
of  vesicles  like  soap-bubbles ;  these  float  in  the  air, 
rising  or  falling  till  they  are  in  equilibrium  with  the  air, 
remaining  suspended  thus  as  long  as  they  preserve  the 
same  state.  When  the  particles  of  vapor  approach 
within  a  certain  distance  of  each  other,  these  minute 
water-drops  have  a  tendency  to  unite,  and  presently  fall 
in  the  shape  of  rain.  Many  of  the  phenomena  in  the 
formation  of  clouds  cannot  be  fully  explained  ;  but  we 
may  be  certain  that,  when  a  cloud  is  formed  in  the  air, 
whatever  be  the  cause,  it  can  subsist  there  only  while 
aqueous  vapors  continue  to  be  produced  in  the  same 
place.  Thus  the  extent  occupied  by  a  cloud  is  an 
indication  of  the  cause  which  produces  vapors,  or  of 
its  intensity  in  some  part  of  this  space.  Extreme 
humidity  exists  but  very  little  beyond  the  extent  of  the 
cloud,  and  as  soon  as  the  cause  which  furnishes  the 
vapor  ceases,  the  cloud  dissipates. 
19* 


222  METEOROLOGY. 

The  evaporation  of  clouds,  even  while  they  are  in- 
creasing in  size,  is  a  circumstance  of  which  we  may 
easily  be  satisfied,  by  considering  attentively  the 
broken  edge  of  a  cloud  which  has  a  clear  sky  behind 
it.  These  edges  present  to  the  eye  a  thousand  gro- 
tesque forms :  often  we  perceive  the  part  on  which  we 
are  gazing  dissipated  in  the  place  where  it  was  first 
observed  ;  often  it  stretches  itself  out,  the  cloud  remain- 
ing stationary,  and  vanishes  while  it  is  thus  extending 
itself.  Sometimes,  while  one  festoon  vanishes,  others 
are  formed,  by  which  the  cloud  is  enlarged  :  at  other 
times,  the  festoons  successively  evaporate,  till  the  whole 
disappears.  It  is  impossible  to  consider  these  various 
metamorphoses  of  the  same  cloud  without  supposing  that 
there  is,  in  the  air,  a  source  of  vapors  which  are  pro- 
duced in  the  place  where  the  cloud  is  formed,  and  that 
it  is  by  the  continual  production  of  fresh  vapor  that  th« 
cloud  subsists  and  increases,  though  continually  evap- 
orating. When  they  wholly  disappear,  it  is  becaus* 
the  evaporation  is  not  repaired  by  the  formation  of 
fresh  vapor.  These  phenomena  are  independent  of 
heat  and  cold ;  for  clouds  are  formed  suddenly  in  the 
middle  of  a  hot  day,  and  after  they  have  poured  down 
their  water,  all  is  clear  again.  Sometimes  they  evap- 
orate after  sunset,  gradually  vanishing,  in  the  calmest 
weather,  without  change  of  place.  The  appearances, 
on  the  whole,  are  such  as  would  be  produced  by  a 
large  mass  of  water,  in  violent  ebullition,  suspended 
invisibly  in  the  atmosphere ;  and  the  similarity  in  the 
effect  naturally  points  out  an  analogy  in  the  cause -- 
that  is,  a  source  of  vapor  in  the  atmosphere. 

When  it  rains,  the  source  which  furnishes   vapors 


MREOBOLOGT.  223 

produces  them  in  such  abundance  that  the  vesicles  are 
driven  against  each  other,  even  in  the  bosom  of  the 
cloud,  and,  not  having  time  either  to  disperse  or  evap- 
orate, they  are  united ;  and  the  water  falling  to  the 
lowest  part,  as  in  soap-bubbles,  they  are  soon  burst,  and 
fall  as  rain.  It  is  to  these  surcharged  vesicles  that  we 
must  attribute  the  pendent  fringes  which  are  sometimes 
seen  under  the  clouds  towards  the  horizon.  Experi- 
ence has  shown  that  it  rains  under  those  clouds :  not 
that  these  fringes  are  rain  itself,  but  the  vesicles  which 
fall  by  the  augmentation  of  their  weight.  As  drops  of 
rain  are  formed,  the  vesicles  are  destroyed.  There  is 
no  sign  of  rain  more  certain  than  two  difFerent  cur- 
rents of  clouds,  especially  if  the  undermost  flies  fast 
before  the  wind.  When  this  happens  in  summer,  there 
is  seldom  wind  at  the  time,  and  thunder  generally  fol- 
lows. In  winter,  the  light  vapor,  or  scud,  as  the  sailors 
call  it,  often  comes  rapidly  against  the  wind,  and  a  gale 
is  expected  soon.  The  transparency  of  the  air  is,  to  the 
inhabitants  of  the  Alps,  one  of  the  most  certain  signs 
of  rain  :  when  distant  objects  appear  distinct  and  well- 
defined,  when  the  sky  is  of  a  deep  blue,  they  consider 
rain  as  near  at  hand,  though  no  other  signs  appear. 
The  same  has  been  remarked  in  England  and  other 
countries.  In  such  a  state  of  the  air,  the  sailors  say 
the  land,  or  other  object,  looms  near,  and  predict  bad 
weather.  In  the  West  Indies,  it  is  observed  that  the 
stars  look  uncommonly  large  immediately  before  a 
hurricane. 

In  Middle  and  Lower  Egypt  it  never  rains,  and  the 
excessive  fertility  arises  from  the  flood  of  the  Nile. 
The  natives  do  not  credit  the  phenomenon  of  water 


224  METEOROLOGY. 

falling  from  above.  Hence  it  is  that  all  monuments 
are  so  nicely  preserved.  Buckingham  found  a  building 
which  was  left  unfinished  3  or  4000  years  since,  with 
the  ocbreous  marks  of  the  workmen  still  perfect.  A 
fog  hangs  for  six  months  over  Peru,  and  rain  so  sel- 
dom falls  that  a  shower  is  a  great  calamity,  since  no 
precautions  are  taken  against  one. 

Dew  is  the  moisture  which  is  deposited  upon  the  sur- 
face of  the  earth,  from  the  air,  in  the  form  of  minute  glob- 
ules, resembling  drops  of  rain.  It  is  only  deposited 
upon  surfaces  colder  than  the  surrounding  air.  Some 
substances  on  the  earth  are  found  to  grow  colder  dur- 
ing the  night  than  others,  and  these  receive  the  greatest 
share  of  dew.  Deep  water,  which  retains  the  heat 
received  during  the  day,  receives  none  at  all ;  and  ani- 
mals sleeping  in  the  open  air  remain  perfectly  dry, 
while  the  grass  around  them  is  covered  with  water. 
Hoar-frost  is  formed  only  upon  very  cold  nights ;  the 
dew  then  freezes,  and  has  a  white  appearance,  like  ice 
or  snow.  Dew  is  generally  more  plentiful  in  spring 
and  autumn  than  in  summer,  because  a  greater  differ- 
ence is  found  between  the  temperatures  of  the  day  and 
night  in  the  former  seasons  than  in  the  latter.  The 
formation  of  dew  may  be  seen,  on  a  smaller  scale,  in 
the  collection  of  drops  and  moisture  on  the  outside  of  a 
tumbler  of  cold  water  upon  a  sultry  day.  The  tum- 
bler, being  colder  than  the  air  around  it,  condenses  the 
air,  and  receives  a  portion  of  its  moisture.  The  an- 
nual deposit  of  dew  is  about  five  inches  deep. 

Snow  is  found  when  the  atmosphere  is  so  cold  as  to 
freeze  the  particles  of  rain  as  soon  as  they  are  formed  • 
and  the  adherence  of  several  of  these  particles  to  each 


METEOROLOGY.  225 

other,  which  meet  and  cling  together  as  they  descend 
through  the  air,  forms  the  usual  fleeces  of  snow,  which 
are  larger  in  proportion  as  the  clouds  are  higher, 
since  they  are  longer  in  descending,  and  have  more 
time  to  accumulate.  By  this  means  the  heat  of  tha 
earth  is  confined,  and  an  admirable  defence  formed  for 
the  vegetable  kingdom  during  the  severities  of  winter. 
Snow-flakes  usually  consist  of  regular  crystals,  pre- 
senting many  curious  forms,  which,  when  viewed 
through  a  microscope,  appear  as  in  the  annexed  cut. 


Snow  has  been  seen,  in  the  polar  regions,  of  a  red, 
orange,  and  salmon  color :  this  occurs  both  on  the 
fixed  and  on  floating  ice,  and  appears  in  some  cases 
to  result  from  vegetable,  and  in  others  from  animal 
matter,  suspended  in  the  sea,  and  deposited  upon  the 
ice  around.  Sometimes,  natural  snow-balls,  an  inch  in 


JSiJb  METEOROLOGY. 

diameter,  are  formed  by  the  rotation  of  the  snow  while 
falling.  Snow-storms  occasionally  present  a  luminous 
appearance  :  one  was  witnessed  in  March,  1813,  by  a 
party  on  Loch  Awe,  in  Scotland,  which  imparted  to  the 
glassy  surface  of  the  lake,  the  boat,  their  clothes,  and 
all  the  surrounding  scenery,  a  luminous  appearance, 
like  a  huge  sheet  of  fire.  Their  own  bodies,  to  the 
eye,  all  seemed  to  burn ;  although,  of  course,  without 
any  feeling  of  warmth.  When  they  applied  their 
hands  to  any  of  the  melting  snow,  the  luminous  sub- 
stance adhered  to  them  as  well  as  the  moisture,  and 
this  property  was  retained  by  the  snow  for  twelve  or 
fifteen  minutes. 


Masses  of  Ice  in  Polar  Regions. 

In  the  polar  regions,  the  cold  is  so  intense  and  inva- 
riable, that  the  ocean  is  generally  encumbered  by  large 
fields  of  ice  ;  and  the  air  is  frequently  loaded  with 


METEOROLOGY.  227 

dense  and  heavy  fogs,  by  which  navigation  is  rendered 
extremely  perilous,  and  consequently,  until  lately,  has 
been  avoided  by  the  most  adventurous  seamen. 

The  formation  of  hail  has  never  yet  been  explained. 
Hail  shows  the  existence  of  an  intense  degree  of  cold ; — 
yet  hailstones  of  an  enormous  size  are  formed  during 
the  hottest  hours  of  the  day  in  the  hottest  months  of 
the  year ;  and  hail  is  more  frequent  in  summer  than  in 
winter.  The  common  notion  is,  that  it  is  caused  by  the 
freezing  of  rain-drops ;  yet  hail  is  usually  formed  in 
clouds  that  are  very  low  in  the  atmosphere.  It  is  highly 
probable  that  electricity  has  some  extraordinary  agency 
m  its  production.  The  descent  of  hail,  in  some  coun- 
tries, appears  to  occur  at  particular  periods.  In  France, 
Italy,  and  Spain,  it  commonly  hails  most  abundantly 
during  the  hottest  hours  of  the  day  in  spring  and  sum- 
mer ;  and  in  Europe  generally,  it  falls  principally  dur- 
ing the  day,  though  there  are  examples  of  great  hail- 
storms which  have  taken  place  during  the  night.  That 
hail-storms  have  definite  limits,  may  be  inferred  from 
the  tremendous  storm  which  desolated  so  great  a  por- 
tion of  France  in  July,  1788.  It  began  in  the  south- 
west, and  proceeded  in  two  parallel  bands  to  the 
north-east,  the  extent  of  one  of  them  being  175  leagues, 
and  of  the  other  200,  —  thus  traversing  nearly  the  whole 
length  of  that  great  kingdom,  and  even  a  portion  of 
the  Low  Countries.  The  mean  breadth  of  the  eastern 
band  was  four  leagues,  and  of  the  western,  two ;  and, 
what  is  very  remarkable,  the  interval  between  the  two 
bands,  amounting  to  five  leagues,  was  deluged  with 
heavy  rain. 

This  tremendous  storm  was  ushered  in  by  a  dread- 


228  METEOROLOGY. 

ful  and  almost  total  darkness,  which  suddenly  over- 
spread the  whole  country.  In  a  single  hour  the  face 
of  nature  was  so  entirely  changed,  that  no  person 
who  had  slept  during  the  tempest  could  have  believed 
himself  in  the  same  part  of  the  world.  Instead  of  the 
smiling  bloom  of  summer,  and  the  rich  prospects  of 
autumn,  which  were  just  before  spread  over  the  country, 
it  now  presented  the  dreary  aspect  of  gloomy  winter 
and  sterility.  The  fertile  soil  was  changed  into  a 
morass  ;  the  standing  corn  beaten  into  a  quagmire  ;  the 
vines  and  the  fruit-trees  were  torn  to  pieces ;  and  the 
hail  lay  in  heaps,  like  rocks  of  solid  ice.  The  damage 
caused,  in  every  part  of  the  course  of  the  storm,  re- 
quired years  for  its  repair.  This  unforeseen  and  irre- 
sistible calamity,  coming  on  when  the  popular  discon- 
tent was  leading  rapidly  to  political  dissensions,  and 
when  all  men  were  looking  for  some  great  convulsion 
in  the  state,  produced  a  singular  effect  upon  the  people, 
•ind  had  much  influence  in  hastening  the  crisis  of  the 
revolution. 

Hailstones  are  sometimes  so  large  as  to  kill  pigeons, 
ducks,  and  geese.  A  case  is  on  record  where  hail- 
stones were  projected  from  a  cloud  almost  horizontally, 
and  their  velocity  was  such  that,  in  many  instances,  a 
clear  round  hole  was  left  in  the  glass  which  they 
pierced,  as  if  a  bullet  had  been  shot  through  it.  In 
referring  hail  to  an  electrical,  origin,  we  may  explain 
the  oblique  discharges  by  supposing  two  electrical 
clouds  drawn  towards  each  other.  Arago  remarks  that 
sometimes,  before  the  descent  of  hail,  a  crackling  noise 
is  heard,  which  it  would  be  difficult  to  describe  in  any 
other  way  than  by  comparing  it  to  the  emptying  a  bag 


METEOROLOGY.  229 

of  walnuts.  This  is  accounted  for,  by  some  meteorolo- 
gists, by  supposing  the  hailstones  to  be  driven  by  the 
wind  against  each  other  in  the  clouds  which  carry 
them.  Others  imagine  the  hailstones  themselves  to  be 
strongly  and  differently  electrified,  and  consider  the 
crackling  in  question  to  result  from  electrical  dis- 
charges a  thousand  times  repeated. 

Thunder  and  lightning,  we  have  already  shown,  are 
caused  by  electricity ;  but  the  cause  of  the  thunder-clap, 
which  accompanies  the  flash,  is  still  the  subject  of  con- 
jecture. In  general,  it  is  considered  that  lightning,  by 
its  heat,  creates  a  partial  vacuum  in  the  atmosphere,  and 
that  the  sudden  rushing  of  air  into  the  void  space  pro- 
duces the  sound ;  but  various  reasons  have  been  as- 
signed for  the  long-continued  noise  of  thunder.  It  was 
formerly  supposed  that  the  rolling  sound  is  merely  the 
result  of  several  echoes  caused  By  reflection  from  moun- 
tains, woods,  buildings,  or  clouds,  or  from  the  latter 
alone  when  a  thunder-storm  takes  place  over  the  ocean. 
This  opinion  seems  to  have  been  founded  upon  the 
fact,  that  the  report  of  a  gun,  discharged  in  a  mountain- 
ous region,  is  prolonged  by  the  echoes  during  at  least 
half  a  minute,  which  is  about  the  time  that  the  rolling 
of  thunder  continues.  But,  though  the  reflections  of 
sound  are  very  probably,  in  part  or  at  times,  the  causes 
of  the  prolongation  of  thunder,  they  do  not  always 
afford  a  satisfactory  explanation  of  the  phenomenon, 
which,  in  a  great  many  cases,  cannot  be  accounted  for 
by  the  doctrine  of  echoes.  Possibly,  the  rolling  may 
arise  from  the  circumstance  that  there  are  several 
points  of  explosion,  at  different  distances  from  the  ear. 

The  flash  of  lightning,  and  the  explosion  of  the 
xin. — 20 


230  METEOROLOGY. 

thunder,  take  place  in  reality  at  the  same  moment ;  but 
as  sound  travels  at  the  rate  of  1125  feet  in  a  second, 
while  the  passage  of  light  from  the  cloud  to  the  ob- 
server may  be  considered  as  instantaneous,  it  follows 
that,  on  counting  the  number  of  seconds  which  elapse 
between  the  time  of  seeing  the  flash  and  hearing  the 
report,  the  distance  of  the  thunder-cloud  from  the  ob- 
server may  be  ascertained,  if  1125  feet  be  multiplied 
by  that  number  of  seconds.  From  the  observations  of 
the  voyagers  toward  the  north  pole,  it  appears  thai 
neither  thunder  nor  lightning  is  known  beyond  the  75th 
degree  of  latitude  ;  and  even  as  high  as  the  70th  degree 
they  are  extremely  rare. 

Winds  are  occasioned  by  whatever  disturbs  the 
equilibrium  of  the  atmosphere,  or  the  equal  density  or 
quantity  of  air  at  equal  distances  from  the  surface  of 
the  earth  —  whatever  accumulates  the  air  in  one  place, 
and  diminishes  it  in  other  places.  Heat,  which  rarefies, 
and  cold,  which  condenses  the  air,  are  by  far  the  prin- 
cipal and  more  general  causes  which  produce  currents 
in  the  atmosphere.  Another  cause  has  been  ascribed 
to  the  attraction  of  the  sun  and  moon,  whose  influence 
is  supposed,  with  great  probability,  to  occasion  a  tide, 
or  flux  and  reflux,  of  the  atmospherical  fluid,  similar  to 
that  of  the  sea,  but  greater,  because  the  air  lies  nearer 
to  those  celestial  bodies,  and  because  air  is  incom- 
parably more  expansible  than  water.  Some  action  in 
the  production  of  the  wind  may  also  be  derived  from 
volcanoes,  fermentations,  evaporations,  and  especially 
from  the  condensation  of  vapors ;  for  we  find  that,  in 
rainy  weather,  a  considerable  wind  frequently  precedes 
the  approach  of  every  single  cloud,  and  that  the  wind 


METEOROLOGY.  231 

subsides  as  soon  as  the  cloud  has  passed  over  the 
zenith. 

Winds  are  phenomena  in  a  great  measure  depend- 
ent on  the  law,  that  lighter  fluids  rise  in  heavier  ones. 
As  oil,  let  loose  under  wafer,  is  pressed  up  to  the  sur- 
face, and  swims,  so  air,  near  the  surface  of  the  earth, 
when  heated  and  expanded  by  the  sun,  rises  to  the  top 
of  the  atmosphere,  and  spreads  there,  forced  up  by  the 
heavier  air  around,  which  rushes  inward,  and  consti- 
tutes wind.  The  cross  currents  in  the  atmosphere,  thus 
arising,  are  often  rendered  evident  by  the  motion  of 
clouds  or  balloons.  If  our  globe  were  at  rest,  and  the 
sun  were  always  shining  on  the  same  part,  the  earth 
and  air  directly  under  him  would  become  exceedingly 
heated,  and  then  the  air  would  be^onstantly  rising,  like 
oil  in  water,  or  the  smoke  from  a  great  fire  —  which 
currents  or  winds  would  be  pouring  towards  the  central 
spot  from  all  directions  below.  But  the  earth  is  con- 
stantly turning  round  under  the  sun,  so  that  the  whole 
middle  region,  or  equatorial  belt,  becomes  heated; 
therefore,  according  to  the  principle  just  laid  down, 
there  should  be  over  it  a  constant  rising  of  air,  and 
constant  currents  from  the  two  sides  of  it,  on  the  north 
and  south,  to  supply  the  ascent.  Now,  this  phenomenon 
is  really  going  on,  and  has  been  going  on  ever  since 
the  beginning  of  the  world,  producing  the  steady  winds 
of  the  northern  and  southern  hemispheres,  called  the 
trade  ivinds,  which  prevail  in  most  places  within  30  de- 
grees of  the  equator,  and  on  which  mariners  reckon 
almost  as  confidently  as  on  the  rising  and  setting  of 
the  sun. 

The  trade  winds,  however,  do  not  appear  on  the  earth 


232  METEOROLOGY. 

to  be  directly  north  and  south,  as  they  are  in  fact ;  for 
the  eastward  whirling,  or  diurnal  rotation,  of  the  earth, 
causes  a  wind  from  the  north  to  appear  as  if  coming 
from  the  north-east,  and  a  wind  from  the  south  as  if 
coming  from  the  south-east.  This  is  illustrated  by  the 
case  of  a  man  on  a  galloping  horse,  to  whom  a  calm 
appears  to  be  a  strong  wind  in  his  face  ;  or,  if  he  is 
riding  eastward,  while  the  wind  is  directly  north  or 
south,  such  wind  will  appear  to  him  to  come  from  the 
north-east  or  south-east.  While,  in  the  lower  regions  of 
the  atmosphere,  air  is  constantly  flowing  towards  the 
equator,  and  forming  the  steady  trade  winds  between 
the  tropics,  in  the  upper  regions  there  must,  of  course, 
be  a  counter-current,  distributing  the  heated  air  over 
the  globe.  This  haabeen  confirmed  by  many  obser- 
vations. At  the  summit  of  the  Peak  of  Teneriffe  there 
is  always  a  strong  wind,  blowing  in  a  direction  contrary 
to  that  of  the  trade  wind  on  the  face  of  the  ocean 
below ;  and,  among  other  proofs,  we  may  specify  the 
following  singular  incident :  — 

On  the  30th  of  April,  1812,  about  midnight,  the  in- 
habitants of  the  Island  of  Barbadoes  were  roused  from 
their  sleep,  and  greatly  alarmed,  by  a  sound  like  that 
of  a  heavy  cannonading,  and  a  light  similar  to  the 
flashes  from  guns  was  seen  in  the  west.  It  was  sup- 
posed to  be  a  naval  action  between  a  British  ano 
French  fleet.  The  troops  were  beat  to  arms,  and  dj 
were  put  in  readiness  to  act  as  the  emergency  might 
require.  The  firing  increased  towards  morning,  but 
afterwards  the  sound  died  away.  All  this  time  the  sky 
was  perfectly  clear  and  serene  ;  but  soon  after  dawn, 
thick  masses  of  clouds  cc7'  ,-cted  over  the  island,  and 


METEOROLOGY.  233 

poured  down,  instead  of  rain,  torrents  of  an  earthy 
dust  finer  than  sand.  The  sun  rose  invisible,  and  all 
nature  was  wrapped  in  darkness  more  intense  than 
ever  was  known  in  the  blackest  midnight.  The  alarm 
of  war  immediately  gave  place  to  more  appalling 
thoughts ;  all  were  thrown  into  indescribable  conster- 
nation. Many  persons  apprehended,  and  not  without 
reason,  that  the  end  of  the  world  had  come ;  and  the 
affrighted  multitude  thronged  to  the  churches,  groping 
their  way  with  lanterns  in  their  hands.  It  was  not  till 
20  minutes  past  noon  that  a  gleam  of  light  afforded  a 
feeble  hope  to  the  dismayed  population.  In  the  after- 
noon, the  falling  of  the  dust  gradually  abated,  and  the 
sky  slowly  became  clear,  and  dissipated  their  fears. 
The  dust  had  fallen  in  some  places  six  inches  in  depth. 
A  ship  500  miles  eastward  of  Barbadoes  had  her  sails 
and  decks  covered  with  it.  On  being  analyzed,  it 
proved  to  be  volcanic  ;  and  5  days  afterwards,  a  vessel 
arrived  from  St.  Vincent's  with  the  intelligence,  that 
the  Souffriere,  a  volcano  in  that  island,  had  burst  forth 
in  flames,  and  laid  the  whole  colony  in  ashes.  All  this 
time  the  regular  trade  wind  had  been  blowing  from  the 
eastward,  which  should  have  carried  the  ashes  away 
from  Barbadoes,  that  island  lying  70  miles  to  windward 
of  St.  Vincent's  ;  but  the  volcano  had  thrown  its  con- 
tents above  the  trade  wind  into  a  contrary  current  of 
air,  and  thus  the  ashes  had  been  transported  upwards 
of  500  miles,  apparently  against  the  wind. 

Beyond  the  tropics,  where  the  heating  influence  of 

the  sun  is  less,  the  winds  occasionally  are  subjected  to 

other  influences  besides  those  which  we  have  described, 

but  which  have  not  yet  boon  well  explained.     Iti  many 

20* 


234  METEOROLOGY 

situations  beyond  the  tropics,  the  westerly  winds,  which 
are  merely  the  upper  equatorial  currents  of  air  falling 
down,  are  almost  as  regular  as  the  easterly  winds 
within  the  tropics.  Voyages  from  the  United  States  to 
Europe  are  usually  shorter  than  voyages  home.  While 
the  sun  is  beaming  directly  over  a  tropical  island,  he 
heats  the  surface  of  the  soil,  and  therefore  the  air  over 
it ;  but  the  rays  which  fall  upon  the  ocean  around, 
penetrate  into  the  water,  and  the  superficial  increase 
of  temperature  is  less.  In  consequence  of  this,  there 
is  a  rapid  ascent  of  hot  air  over  the  island  during  the 
day,  and  a  cooler  wind  blowing  towards  its  centre  from 
all  points.  This  wind  constitutes  the  refreshing  sea- 
breeze  of  tropical  islands  and  coasts.  During  the  night, 
an  opposite  phenomenon  takes  place.  The  surface  of 
the  earth,  then  no  longer  receiving  the  sun's  rays,  is 
soon  cooled,  while  the  sea,  which  absorbed  heat  during 
the  day,  not  on  the  surface  only,  but  through  its  mass, 
continues  to  give  out  heat  all  night.  The  consequence 
is,  that  the  air  over  the  earth,  being  colder  than  that  over 
the  sea,  sinks  down  and  spreads  out  on  all  sides,  pro- 
ducing the  land-freeze  of  tropical  climates.  This 
wind  is  often  charged  with  noxious  exhalations  from 
the  marshes  and  forests,  while  the  sea-breeze  is  all 
purity  and  freshness.  Many  islands  and  coasts  would 
be  totally  uninhabitable  but  for  their  sea-breezes. 

In  the  East  Indian  seas  a  periodical,  or  trade  wind, 
called  the  monsoon,  blows  half  the  year  in  one  direc- 
tion, and  half  the  year  in  the  opposite.  These  direc- 
tions are  different  in  different  places  ;  in  some  north 
and  south,  in  others  north-east  and  south-west.  The 
change  of  the  monsoon  is  announced  by  calms  and 


METEOROLOGY.  235 

squalls  in  rapid  succession,  waterspouts,  tornadoes, 
and  hurricanes  called  taifouns  or  tuffoons,  particularly 
terrible  from  the  explosions  of  electric  matter  accu- 
mulated during  the  monsoon. 

We  come  now  to  the  most  interesting  and  important 
subject  in  meteorology — the  philosophy  of  storms  and 
hurricanes ;  and  here  it  is  somewhat  mortifying  to  the 
pride  of  science,  that  we  know  so  little  of  the  true 
cause  of  these  terrible  perturbations  of  the  atmosphere. 
When  the  paroxysms  of  heat  and  cold  smite  the  organ* 
izations  of  animal  and  vegetable  life ;  when  the  swollen 
cloud  pours  down  its  liquid  charge,  and  menaces  us  with 
A  second  deluge ;  when  the  raging  tempest  sweeps  over 
the  earth  with  desolating  fury ;  when  the  electric  fires 
shiver  the  fabrics  of  human  power,  and  rend  even  the 
solid  pavement  of  the  globe,  —  when  all  the  powers  of 
the  air  are  thus  marshalled  against  him,  man  trembles 
upon  his  own  hearth,  the  slave  of  terrors  which  he 
cannot  foresee,  the  sport  of  elements  which  he  cannot 
restrain,  and  the  victim  of  desolation  from  which  he 
knows  not  how  to  escape. 

The  East  and  West  Indies  are  the  countries  in 
which  hurricanes  most  frequently  exercise  their  ray- 
ages.  The  hurricanes  of  the  northern  parts  of  the 
globe  are  not,  in  any  way,  to  be  compared  to  those  of 
the  equatorial  regions.  Generally  speaking,  the  former 
are  nothing  more  than  whirlwinds  occasioned  by  the 
meeting  of  two  opposite  currents.  But,  in  a  real  hurri- 
cane, all  the  elements  seem  to  have  combined  and 
armed  themselves  for  the  destruction  of  nature.  The 
lightnings  cross  each  other,  the  thunder  roars  without 
interval,  rain  falls  in  torrents,  and  the  velocity  of  the 


236  METEOROLOGY. 

wind  far  exceeds  that  of  a  cannon-ball.  A  West 
India  hurricane  is  generally  preceded  by  an  awful  still- 
ness of  the  elements ;  the  air  becomes  close  and  heavy, 
the  sun  is  red,  and  the  stars  at  night  seem  unusually 
large.  Frequent  changes  take  place  in  the  barometer 
and  thermometer;  darkness  extends  over  the  earth; 
the  higher  regions  gleam  with  lightning.  Sometimes,  a 
little  black  cloud  appears  on  the  summit  of  a  mountain ; 
and  at  the  instant  when  it  seems  to  settle  on  the  peak, 
it  rushes  down  the  declivity,  spreads  out,  and  covers  all 
the  horizon.  At  other  times,  the  tempest  advances  in 
the  semblance  of  a  fire-colored  cloud  showing  itself 
suddenly  in  a  calm  and  serene  sky. 

The  most  celebrated  hurricane  on  record  is,  perhaps, 
that  which  desolated  the  Island  of  Barbadoes  in  1831, 
and  was  attended  by  the  most  singular  meteorological 
phenomena  ever  witnessed.  The  month  of  July,  in 
that  quarter,  had  been  more  than  usually  rainy ;  but 
the  trade  wind  blew  moderately  and  steadily  from  the 
proper  quarter,  and  the  temperature  was  remarkably 
uniform.  Much  thunder  and  lightning  occurred  toward 
the  end  of  the  month,  and  in  the  first  week  of  August. 
On  the  10th  of  August,  the  sun  rose  without  a  cloud, 
and  shone  resplendently  through  an  atmosphere  of  the 
most  translucent  brightness.  Calms,  and  slight  puffs 
of  wind,  prevailed  throughout  the  day,  and  the  ther- 
mometer stood  at  88  in  the  afternoon.  At  5  o'clock, 
the  clouds  began  to  gather  fast  in  the  north,  and  the 
wind  commenced  blowing  strong  from  that  point.  A 
shower  of  rain  fell,  after  which  there  was  a  remarkable 
stillness,  made  more  impressive  by  the  dismal  darkness 
of  the  clouds  on  the  horizon  all  around.  This  dark, 


METEOROLOGY.  237 

impenetrable  body  extended  up  toward  the  zenith, 
leaving  there  an  obscure  circle  of  light  of  a  dismal 
hue,  which  remained  at  rest  but  a  few  seconds  only, 
when  the  scud  of  the  cloud  was  seen  in  a  state  of 
ebullition.  The  dense  mass  around  was  also  agitated 
and  separating,  and  bodies  of  it  were  dispersed  to  all 
points  of  the  compass.  At  7  in  the  evening,  the  sky 
was  clear  again,  and  the  air  calm.  At  10,  came  on 
showers,  lightning,  and  squalls ;  after  midnight,  the 
continual  flashing  of  the  lightning  was  awfully  grand, 
and  a  fierce  gale  blew  from  the  north-east. 

But  these  phenomena  were  slight  in  comparison  to 
what  soon  followed.  At  1  in  the  morning,  the  tem- 
pestuous rage  of  the  wind  increased,  and  the  storm 
shifted  suddenly  to  the  north-west.  The  upper  regions 
of  the  air  were  from  this  time  illuminated  by  incessant 
lightning  ;  but  the  quivering  sheet  of  blazing  fire  was 
far  surpassed  in  brilliancy  by  the  darts  of  the  electric 
fluid,  which  were  exploded  in  every  direction.  A  little 
after  2  o'clock,  the  astounding  roar  of  the  hurricane 
came  on  with  a  terrible  impetuosity  that  no  language 
can  describe,  nor  mind  conceive.  Those  who  wit- 
nessed it  compared  it  to  the  agonizing  shrieks  of  mil- 
lions of  human  beings  in  the  last  horrors  of  despair 
and  they  affirm  that  there  was  something  indescribably 
piercing  and  heart-rending  in  this  wailing  scream, 
which  never  ceased  till  the  end  of  the  hurricane. 
About  3,  the  wind  occasionally  abated,  but  only  to 
return  in  gusts  from  the  south-west,  west,  and  north- 
west, with  accumulated  fury.  It  was  now  that  the 
most  portentous  and  appalling  apparitions  added  new 


238  METEOROLOGY. 

horrors  to  the  scene.  The  heavens  appeared  all  in 
flames,  with  balls  of  fire  flying  in  all  directions,  and 
bursting  like  shells  from  a  mortar.  One  of  them  was 
seen  of  a  globular  form,  and  deep-red  hue,  descending 
perpendicularly  from  a  great  height;  on  approaching 
the  earth,  its  motion  was  accelerated,  it  became  of  a 
dazzling  whiteness,  and  elongated  in  form,  —  and,  dash- 
ing on  the  ground  in  one  of  the  paved  squares  of  Bridge- 
town, it  splashed  around  in  the  same  manner  as  melted 
lead  would  have  done  if  thrown  out  of  a  furnace,  and 
became  instantly  extinct,  though  the  brilliancy  and 
spattering  of  its  particles,  when  it  reached  the  earth, 
gave  it  the  appearance  of  a  giobe  of  quicksilver. 

A  few  minutes  after  the  appearance  of  this  phe- 
nomenon, the  deafening  noise  of  the  wind  sank  into  a 
solemn  murmur,  like  a  distant  roar;  and  the  lightning, 
which,  since  midnight,  had  played  in  flashes  and  forked 
darts  with  scarcely  any  intermission,  seemed,  for  half  a 
minute,  to  hover  between  the  clouds  and  the  earth, 
moving  frightfully,  and  with  a  novel  and  surprising 
action.  There  seemed  to  be  a  vast  body  of  vapor, 
almost  touching  the  houses,  which  apparently  caught 
fire  from  the  clouds,  and  conveyed  it  flaming  down- 
wards, while,  again,  a  thousand  torches  were  lighted 
from  the  earth,  and  mounted  to  the  sky.  While  this 
strange  phenomenon  continued,  the  earfh  was  felt  to 
vibrate  in  a  manner,  and  in  time,  answering  with  the 
action  of  the  lightning.  Twice,  or  more,  when  the 
coruscations  were  more  brilliant  and  severe,  but  less 
rapid  in  their  motion,  the  earth  received  corresponding 
shocks.  The  moment  this  singular  alternation  of  the 
lightning  passing  to  and  from  the  earth  ceased,  the 


METEOROLOGY.  239 

hurricane  again  burst  from  the  west,  with  a  violence 
exceeding  all  that  had  as  yet  been  experienced,  and 
hurling  every  thing,  in  fragments,  before  it.  Masses 
of  lead  weighing  400  pounds  were  carried  above  a 
quarter  of  a  mile ;  the  strongest  buildings  vibrated  to 
their  foundations,  and  the  very  surface  of  the  earth 
trembled  as  the  destroying  blast  passed  over  it  The 
storm  absolutely  out-roared  the  thunder,  and  the  latter 
was  not  even  heard.  All  witnesses  concur  in  affirming 
that,  had  the  cannon  of  a  thousand  batteries  been 
discharged,  their  sound  could  not  have  been  distin- 
guished, so  overpowering  was  the  roar  of  the  wind,  and 
the  howling  of  the  tumultuous  ocean,  whose  frightful 
waves  threatened  to  sweep  into  the  abyss  all  that  the 
other  elements  might  spare. 

Those  who  describe  this  scene  declare  it  to  be  im- 
possible to  express,  in  language,  the  sensations  which 
then  distracted  and  benumbed  their  faculties.  The  sight 
and  hearing  were  overpowered  by  the  horrors  around 
them,  and  many  even  lost  their  senses.  One  person,  on 
coming  to  himself,  found  that  he  was  standing  up  against 
the  wall  of  the  room  in  which  he  was  sleeping  when 
the  hurricane  commenced;  the  roof,  and  every  article 
in  the  room,  had  been  carried  away ;  how  he  escaped 
destruction  he  knew  not !  After  5  o'clock,  there  were 
occasional  lulls  in  the  storm  —  during  which,  the  falling 
of  substances  which  had  been  carried  high  into  the  air, 
the  shrieks  of  suffering  victims,  the  cries  of  the  terrified 
inhabitants,  and  the  mournful  howling  of  the  dogs, 
were  all  distinctly  heard,  and  awakened  in  the  mind  of 
the  listener  a  fearful  appreciation  of  the  scenes  of 
death  and  misery  by  which  he  was  surrounded.  At 


240  METEOROLOGY. 

10  in  the  morning,  the  sun  looked  out  upon  a  scene  of 
devastation  such  as,  perhaps,  was  never  before  wit- 
nessed. The  humble  cot,  and  the  most  costly  mansion, 
had  been  alike  hurled  to  destruction.  Parents  beheld 
their  children,  and  children  their  parents,  buried  in 
ruins,  or  their  disfigured  corpses  strewed  around. 
Others,  with  fractured  limbs  and  dreadful  mutilations, 
were  still  alive,  under  fallen  buildings,  uttering  heart- 
rending cries  of  agony.  Between  2000  and  3000  per- 
sons were  killed  or  mortally  injured,  and  the  wounded 
exceeded  5000.  Houses  were  lifted  up  from  their 
foundations,  and  thrown,  in  one  mass  of  ruins,  into  the 
roads.  Masses  of  rubbish  and  fragments  were  scat- 
tered in  every  quarter.  The  whole  face  of  the  island 
was  laid  waste ;  scarcely  any  sign  of  vegetation  ex- 
isted ;  and  what  remained  was  of  a  sickly-green  color. 
The  surface  of  the  earth  appeared  as  if  fire  had  passed 
over  it,  scorching  and  burning  up  every  thing.  The 
few  trees  that  were  left  standing  were  stripped,  and  the 
bare,  withered  trunks  were  all  that  remained. 

There  are  other  phenomena  in  hurricanes  which 
have  been  in  part  explained  by  the  researches  of  men 
of  science  who  have  recently  turned  their  attention 
to  this  subject.  Sometimes,  a  perfect  calm  happens 
in  the  midst  of  the  tempest,  after  which  it  comes  on 
again  as  furiously  as  ever,  and  in  a  direction  opposite 
to  the  first.  The  master  of  a  ship  lying  at  the  Island 
of  St.  Thomas  says,  "  In  the  morning,  the  wind  was 
north  and  north-west ;  in  the  afternoon,  violent  squalls 
forced  me  to  anchor  in  10  fathoms'  water.  At  5,  the 
squalls  were  succeeded  by  a  gale,  and  at  7  a  hurricane 
arose,  beyond  all  description  dreadful.  The  windlass 


METEOROLOGY.  241 

capsized,  and  I  could  not  slip  my  cables,  the  ship 
driving  till  I  was  in  20  fathoms  of  water  A  calm  then 
succeeded  for  about  10  minutes ;  and  then,  in  the  most 
unearthly  screech  I  ever  heard,  it  recommenced  from  the 
south  and  south-west"  In  another  hurricane,  the  wind 
blew  above  12  hours  with  the  utmost  fury  from  the 
north-east,  and  then,  in  an  instant,  a  perfect  calm  ensued 
for  an  hour.  Then,  "  quick  as  thought,  the  hurricane 
sprang  up  with  tremendous  force  from  the  south- 
west, no  swell  whatever  preceding  the  convulsion. 
The  wind  resembled  numberless  voices,  elevated  to  the 
shrillest  tone  of  screaming."  To  another  vessel  which 
was  caught  in  this  hurricane,  a  most  extraordinary  phe- 
nomenon presented  itself  to  windward,  almost  instan- 
taneously. It  resembled  a  solid,  black,  perpendicular 
wall,  about  15  or  20  degrees  above  the  horizon,  and 
disappeared  almost  in  a  moment.  It  then  reappeared  as 
suddenly,  and  in  5  seconds  was  broken  and  spread  as 
far  as  the  eye  could  see.  The  narrator  describes  this  as 
the  most  appalling  sight  which  he  had  ever  seen.  An 
officer,  on  board  a  British  ship  of  war,  in  describing  a 
hurricane  which  overtook  her  on  the  American  coast, 
in  1814,  states  that,  after  the  wind  had  blown  4  hours, 
with  a  tremendous  sea,  the  barometer  sank  very  low, 
and  the  scenery  of  the  sky  became  indescribable.  "  No 
horizon  appeared,  but  only  something  resembling  an 
immense  wall  within  10  yards  of  the  ship.  She  was 
immediately  thrown  upon  her  beam-ends,  and  the  top- 
masts were  blown  away  without  any  person  hearing 
the  crash."  But  perhaps  the  most  remarkable  phe- 
nomenon exhibited  by  a  hurricane  was  in  1837,  and 
described  by  Captain  Seymour,  of  Cork.  "  For  nearly 
p  sin.— 21 


242  METEOROLOGY. 

an  hour  we  could  not  see  each  other,  nor  any  thing 
else,  but  merely  the  light ;  and,  most  astonishing,  every 
one  of  our  finger-nails  turned  quite  black,  and  re- 
mained so  nearly  5  weeks  afterwards."  This  fact 
may  be  classed  among  other  proofs  of  the  agency  of 
electricity  in  the  production  of  hurricanes. 

Great  light  has  recently  been  thrown  upon  this 
subject  by  the  labors  of  our  ingenious  countryman,  Mr. 
Redfield,  of  New  York ;  and  it  is  now  rendered  ex- 
tremely probable,  if  not  quite  certain,  by  a  .body  of 
evidence  collected  by  him,  that  in  all  or  most  of 
the  great  storms  which  agitate  our  atmosphere,  the 
wind  has  a  rotatory  movement ;  that  the  diameter  of 
the  circle  within  which  the  gyration  is  performed  is 
sometimes  several  hundred  miles ;  and  that  this  whirl- 
wind has  a  progressive  as  well  as  revolving  motion. 
Thus,  in  the  gale  of  the  15th  of  December,  1839,  the 
wind  was  easterly  at  Boston,  Newburyport,  Portsmouth, 
and  Portland ;  northerly  along  the  course  of  the  Hud- 
son ;  south-easterly  at  Nantucket ;  westerly  at  sea 
farther  south ;  and  in  corresponding  directions  at  the 
intermediate  points.  By  marking  down  these  upon  a 
map,  the  circular  shape  of  the  storm  is  fully  demon- 
strated ;  and  we  ascertain  the  important  fact,  that  the 
direction  of  the  wind  at  a  particular  place  forms  no 
part  of  the  essential  character  of  the  storm,  which  is, 
in  all  cases,  compounded  of  both  its  rotatory  and  pro- 
gressive velocities. 

It  appears  that  the  violent  gales  which  are  experi- 
enced on  the  coast  of  the  United  States  are  prolonga- 
tions of  the  West  India  hurricanes  or  whirlwinds. 
They  originate  among  those  islands,  covering  simulta- 


METEOROLOGY.  243 

I 

neously  an  extent  of  surface  from  100  to  500  miles  in 
diameter,  acting  with  great  energy  near  the  centre,  but 
with  diminished  violence  at  the  exterior.  South  of  the 
30th  degree  of  latitude,  these  whirlwinds  move  west- 
erly, gradually  inclining  to  the  north  till  they  approach 
the  30th  parallel,  when  their  course  changes  abruptly  to 
the  north  and  eastward,  the  track  continuing  to  incline 
gradually  to  the  east,  towards  which  point  they  continue 
to  advance  with  an  accelerated  velocity.  Thus,  to  spe- 
cify one  out  of  numerous  examples :  —  In  1804,  a  hurri- 
cane swept  over  the  Windward  Islands  on  the  3d  of 
September ;  the  Virgin  Islands  on  the  4th  ;  Turk's  Island 
on  the  5th  ;  the  Bahamas  on  the  6th  ;  the  coast  of  Geor- 
gia and  Carolina  on  the  7th ;  Virginia,  Maryland,  and 
New  Jersey,  on  the  8th  ;  Massachusetts,  Maine,  and  New 
Hampshire,  on  the  9th,  —  becoming  a  violent  snow-storm 
on  the  White  Mountains.  It  performed  a  journey  of 
2200  miles  in  about  six  days,  at  the  average  rate  of 
about  fifteen  miles  and  a  half  per  hour.  More  violent 
hurricanes  have  travelled  at  double  this  speed. 

In  these  whirlwinds,  the  rotatory  movement  is  always 
from  right  to  left,  or  contrary  to  the  movement  of  the 
hands  of  a  watch  ;  in  the  storms  of  the  southern  hemi- 
sphere, the  reverse  is  tho  case.  Knowing,  therefore,  the 
direction  in  which  the  storm  is  travelling,  a  ship-master, 
on  being  overtaken  by  it,  may  shape  his  course  so  as  to 
sail  out  of  it,  or  towards  the  exterior  edge,  where  its 
violence  is  least.  From  a  lack  of  this  knowledge,  many 
a  ship  has  been  steered  into  the  heart  of  a  storm,  and 
lost,  when  she  might  have  escaped  by  taking  a.  contrary 
direction.  In  the  very  centre  of  the  vortex  is  a  calm 


244  METEOROLOGY. 

| 

spot;  and  whenever  this  passes,  the  phenomenon  occurs, 
which  we  have  already  described,  of  the  wind  falling 
suddenly  calm,  and  then  springing  up  from  the  opposite 
quarter  with  the  same  fury  as  at  first :  this  is  perfectly 
explained  on  the  supposition  of  a  gyrating  circle.  The 
barometer  always  falls  in  the  beginning  of  a  storm,  and 
continues  to  fall  till  the  centre  of  the  circle  has  passed, 
after  which  it  rises.  This  is  ascribed  to  the  centrifugal 
tendency  of  the  immense  revolving  mass  of  atmosphere 
that  constitutes  a  storm,  which  action  must  expand  and 
spread  out  the  stratum  of  air  exposed  to  its  influence. 
The  nature  of  the  soil  over  which  the  wind  blows 
has  a  great  effect  upon  the  quality  of  the  air.  The 
vast  sandy  deserts  of  Africa  and  Arabia  give  a  burning 
heat  and  a  blasting  quality  to  the  air  that  passes  over 
them.  On  the  coast  of  Guinea,  there  is  a  wind  from 
the  interior  called  the  harmattan,  which  scorches  the 
skin  of  those  who  are  suddenly  smitten  by  it  like  a 
blast  from  a  furnace.  An  extraordinary  scorching  wind 
is  felt  occasionally  at  the  Falkland  Islands.  It  cuts 
down  the  herbage  like  a  fire  :  the  leaves  are  parched, 
and  crumble  to  dust :  fowls  are  seized  with  cramps  so 
as  never  to  recover ;  and  men  are  oppressed  with  sore 
throats  and  difficulty  of  breathing.  But  more  dreadful 
than  all  others  is  the  samiel,  or  simoom,  the  deadly 
wind  of  the  deserts  of  Arabia  and  Africa.  The 
camels,  either  by  instinct  or  experience,  have  warning 
of  its  approach,  and  announce  it  by  an  unusual  noise, 
and  by  covering  up  their  noses  in  the  sand.  To  escape 
its  effects,  travellers  throw  themselves  on  the  ground 
•with  their  faces  downward,  and  wait  till  it  has  passed 


METEOROLOGY.  245 

by,  which  is  commonly  in  a  few  minutes,  although  it 
sometimes  continues  much  longer.* 

The  AURORA  BOREALIS,  or  NORTHERN  LIGHTS,  will 
occur  to  the  reader  as  the  most  splendid  of  all  meteor- 
ological phenomena.  They  appear  in  the  northern  part 
of  the  heavens  for  the  most  part,  and  generally  in  frosty 
weather.  Somo  very  splendid  exhibitions  of  this  phe- 
nomenon have  re  <--•'  /  jeen  witE3"sed  in  the  United 
Stuf  DO  ;  but  in  geu  ,  '  we  have  but  a  faint  notion  of  the 
brilliancy  and  m; -j.-'iceuce  with  which  it  appears 
in  the  northern  parts  of  the  globe.  In  the  Shetland 
Islands,  merry  dancers,  as  they  are  cal'  :d  are  the 
constant  attendants  of  clear  evenings,  and  p  j\e  a  great 
relief  amid  the  gloom  of  the  long  winter  nights.  They 
commonly  appear  at  twilight,  near  the  horizon,  of  a 
dun  co'or ;  sometimes  continuing  in  that  state  for 
several  1  ;'jrs  without  any  sensible  motion ;  after  which 
they  break  out  into  streams  of  stronger  light,  spreading 
into  columns,  and  altering  into  ten  thousand  shapes  and 
colors.  They  often  cover  the  whole  heavens,  and 
amaze  the  beholder  with  the  rapidity  of  their  motion 
and  change  of  form  ;  they  com.,  lonly  have  a  strong 
tremulous  motion  from  end  to  end.  Sometimes  they 
assume  a  deep  blood-red  color,  and  strike  a  great  terror 
into  the  spectators. 

Hardly  any  phenomenon  has  excited  more  curiosity 
than  the  aurora  borealis ;  yet  we  know  little  more  of 
its  cause  than  the  fact  that  electricity  has  a  share  in  it. 
It  was  a  much  more  rare  appearance  formerly  than 

•  For  an  example  of  the  dreadful  effects  of  the  simoom^  we 
"Lights  and  Shadcnrs  of  African  History,"  p.  198. 
21* 


246  METEOROLOGY. 

at  present.  In  England,  it  was  hardly  seen  during 
the  whole  of  the  17th  and  the  early  part  of  the  18th 
century.  In  Sweden,  where  it  is  now  almost  perpet- 
ual, it  was  a  great  rarity  before  1716.  There  is  also 
an  aurora  australis,  or  southern  light,  in  the  southern 
polar  regions ;  but  it  is  neither  so  common  nor  so 
brilliant  as  that  of  the  north. 


CHEMISTRY. 


CHEMISTRY  is  that  science  which  investigates  th» 
mutual  agencies  of  the  elementary  principles  of  matter. 
It  attempts  the  resolution  of  all  compound  bodies  into 
their  simple  constituent  parts;  and  it  examines  the 
action  of  these  elements  upon  each  other,  as  well  in  their 
simple  state  as  in  their  varied  forms  of  combination. 
Chemistry  acquaints  us  with  the  means  of  performing 
the  most  important  changes  in  the  properties  of  bodies. 
It  is  a  science,  the  utility  of  which  is  as  boundless  as 
its  extent  The  growth  and  preparation  of  articles  of 
food,  and  every  process  on  which  the  comforts  of  life 
and  the  daily  labor  of  man  are  dependent,  can  improve 
only  with  our  knowledge  of  the  properties  of  bodies 
which  are  the  instruments  we  must  use  to  minister  to 
our  wants. 

Chemistry,  according  to  th«  definition  which  we 
have  given  of  it,  is  a  science  of  but  recent  date,  and 
can  scarcely  be  said  to  have  existed  above  two  centuries. 
But  it  has  been  usual  to  connect  its  history  with  the 
science  of  alchemy,  or  the  supposed  art  of  transmuting 
baser  metals  into  gold,  and  of  preparing  a  universal 
medicine.  Many  alchemists  professed  to  have  obtained 
the  secret  of  metallic  transmutation,  and,  by  the  help 
of  skilful  legerdemain,  some  well-attested  instances  of 
their  successful  operations  are  on  record.  Few,  how- 


248  CHEMISTRY. 

ever,  were,  like  Paracelsus,  bold  enough  to  declare  that 
they  had  discovered  the  elixir  of  life,-,  by  which 
human  existence  might  be  prolonged  to  an  indefinite 
period  of  duration.  It  is  needless  to  say  that  these 
few  gave  an  unfavorable  proof  of  their  success  by 
living  no  longer  than  common  mortals.  Yet  even 
these  were  not  without  some  reason  in  their  folly,  for 
the  operations  of  chemistry  had  recently  so  prepared 
some  metallic  bodies  as  to  render  their  effects  little 
short  of  miraculous  in  arresting  the  progress  of  dis- 
ease ;  therefore  they  might  well  hope  to  see  still 
greater  effects  produced  by  further  investigations.  Al- 
chemy is,  therefore,  considered  the  parent  of  chemistry, 
although  the  objects  of  the  two  sciences  differed  ma- 
terially. The  chemists  found  the  instruments  of  the 
alchemists  ready  fitted  to  their  hands  :  they  found,  also, 
some  useful  facts  recorded,  though  their  number  was 
by  no  means  equivalent  to  the  lator  pnd  the  time  that 
had  been  expended  in  amassing  t!i(Mi.  \'  the  dawn  of 
chemical  science,  the  wisest  of  i!<<"  .  '  '  ^'sts.  qrittir"' 
their  ancient  chimerical  pursuits,  embarked  in  the  '"  iii- 
imate  process  of  ex;  :rimei  ial  chemistry. 

The  alchemists,  fiom  n.  desire  to  conceal  their  self- 
delusion,  or  to  cv'r'o  ;-  -Imiraiion  by  the  appearance 
of  having  accomplished  their  designs,  were  anxious 
to  give  every  product  of  their  laboratories  a  mys- 
terious, extraordinary,  or  unintelligible  name.  °tich 
designations  as  horn  moon,  mercury  of  life,  the  won.' 
derful  salt,  and  the  salt  of  many  virtues,  form  but 
a  small  specimen  of  a  prodigious  number  of  names 
equally  inappropriate  and  ridiculous.  Hence,  when 
\he  dreams  of  alchemy  were  broken  by  the  dawn 


CHEMISTKY.  249 

of  a  more  enlightened  day,  when  men  who  had  the 
promulgation  of  truth  only  for  their  object  became 
chemists  from  a  persuasion  of  the  advantages  which 
the  cultivation  of  that  science  would  afford  to  mankind, 
they  found  it  difficult  to  unravel  the  confusion  caused  by 
the  absurd  names  thus  bestowed  upon  the  materials  of 
their  science.  This  evil  was  not  completely  remedied 
till  toward  the  close  of  the  last  century,  when  the 
French  chemists  took  the  lead  in  reforming  the  chem- 
ical nomenclature,  and  bestowing  upon  all  substances 
significant,  systematic,  and  philosophical  names. 

To  acquire  a  knowledge  of  those  properties  of 
matter,  the  investigation  of  which  belongs  to  chem- 
istry, two  methods  are  employed.  The  one  is  that 
of  analysis,  or  decomposition ;  the  other  is  that  of 
synthesis,  or  composition.  By  the  one,  the  different 
simple  substances  of  which  compound  bodies  consist 
are  separated,  and  their  properties  individually  ex- 
amined ;  by  the  other,  the  simple  substances  are  com- 
bined together,  and  the  properties  of  the  new  com- 
pound are  investigated.  Different  modes  of  analysis 
have  been  admitted  and  described  by  chemical  writers. 
Some  bodies,  when  exposed  to  the  action  of  heat  and 
air,  undergo  a  total  separation  of  their  component 
parts ;  this  is  calfed  spontaneous  analysis  ;  —  thus  some 
minerals,  and  all  vegetable  and  animal  matters,  when 
deprived  of  life  in  favorable  circumstances,  slowly 
separate  into  their  component  parts ;  and  in  the  same 
way,  the  principles  of  which  some  liquids  are  com- 
posed react  on  each  other,  and  spontaneously  separate, 
thus  giving  an  opportunity  of  investigating  the  nature 
of  these  substances. 


250  CHEMISTRY. 

Analysis  by  fire  operates  by  the  accumulation  of 
caloric  in  bodies,  and  by  the  power  which  it  has  of 
separating  their  particles,  thus  favoring  their  examina- 
tion. Another  mode  of  analysis  is  by  re-agents. 
This  is  conducted  by  placing  the  compound  body, 
which  is  to  be  examined,  in  contact  with  various  sub- 
stances which  have  the  power  of  separating  its  con- 
stituent parts ;  this  is  always  done  by  forming  a  com- 
bination with  one  of  the  constituents,  to  the  exclusion  of 
others.  It  is  here  that  the  genius  and  science  of  the 
chemist  appear  most  conspicuous ;  for  every  substance 
in  nature,  and  all  the  products  of  art,  become  valuable 
instruments,  in  his  hands,  to  ascertain  the  nature  and 
investigate  the  properties  of  the  substances  which  come 
under  his  examination. 

Synthesis,  or  composition,  is  the  union  of  two  or 
more  simple  substances.  This  union,  from  whence  a 
new  compound  results,  has  become  an  important  step 
in  exploring  the  properties  of  bodies,  and  in  forming 
a  number  of  products  useful  in  the  arts,  and  necessary 
to  our  wants  ;  and  thus  it  is  considered  by  chemists  — 
being  in  some  measure  the  inverse  of  the  method  of 
analysis  —  as  the  perfection  of  their  art,  and  one  of 
the  great  instruments  of  their  operations.  The  method 
of  synthesis  is,  in  reality,  more  frequently  employed 
than  that  of  analysis ;  and  the  name  of  the  science,  if 
we  regard  these  two  methods,  should  rather  be  the 
science  of  synthesis  than  the  science  of  analysis. 
There  are  many  bodies  which  have  never  yet  been 
decomposed ;  and  it  is  only  by  combining  them  with 
others,  and  examining  the  nature  of  the  compounds 


thus  formed,  that  the  chemical  properties  of  these 
bodies  can  be  investigated. 

Bodies  exist  in  three  different  states,  which  are  quite 
distinct  from  each  other, — namely,  the  solid,  the  fluid, 
and  the  fluid-elastic  state.  Solidity  is  supposed  to  bo 
the  consequence  of  the  irregular  figure  of  the  atoms 
of  matter,  and  their  great  deviation  from  the  spherical 
form,  by  which  free  motion  among  them  is  prevented. 
The  atoms  of  fluid  bodies  are  supposed  to  be  spherical, 
and  their  forces  are  more  directed  to  their  centres  lhaa 
to  their  surfaces,  by  which  motion  is  freely  allowed 
when  any  force  is  applied.  Fluids  are  divided  into 
three  kinds :  one  in  which  the  particles  have  no  mutual 
power,  as  sand  and  fine  powders ;  one  in  which  they 
hare  a  repulsive  power — such  are  the  elastic  fluids,  as 
air;  and  the  third,  in  which  they  have  an  attractive 
power,  as  water,  mercury,  <fcc. 

There  is  also  a  class  of  bodies  intermediate  between 
the  solids  and  fluids ;  these  are  the  viscid  substances, 
the  particles  of  which  attract  each  other  more  strongly 
than  the  fluids,  but  not  so  strongly  as  the  solids.  In 
these  bodies,  the  particles  deviate  so  far  from  the  spher- 
ical form  as  to  produce  a  certain  resistance  among 
each  other,  and  to  impede  their  relative  motion. 

According  to  the  above  explanations,  all  chemical 
phenomena  may  be  traced  to  the  same  principle  — 
namely,  the  law  of  the  forces,  and  the  differences  in 
the  particles  which  thus  arise.  Solution^  for  instance, 
is  thus  explained.  The  particles  of  some  solid  bodies 
have  less  attraction  for  each  other  than  for  the  particles 
of  some  fluids ;  and,  consequently,  when  these  are  ap- 
plied to  each  other,  the  pai  kles  of  tb*  solid  separate. 


252 


CHEMISTRY. 


and  combine  with  those  of  the  fluid,  forming  a  mixture 
of  the  two.  But  the  separation  of  the  particles  of  the 
solid  can  only  take  place  so  long  as  the  particles  of  the 
fluid  are  in  the  sphere  of  their  attraction ;  and  when 
either  of  them  get  beyond  it,  or  when  the  attraction  of 
the  mixture  thus  formed  becomes  equal  to  the  attrac- 
tion of  the  particles  of  the  solid  for  each  other,  no 
further  solution  takes  place,  and  the  fluid  is  said  to  be 
saturated.  But  if  into  this  mixture  another  solid,  whose 
particles  have  a  greater  attraction  for  the  fluid,  be  in- 
troduced, the  fluid  will  leave  the  former  solid,  and 
combine  with  "the  particles  of  the  latter  :  the  particles 
of  the  former  will  fall  to  the  bottom,  and  precipitation 
will  take  place. 

Substances  which  are  dissolved  may  not  only  be  ob- 
tained again  by  precipitation,  but  also  by  slowly  ab- 
stracting part  of  the  fluid  in  which  they  are  dissolved. 
This  is  called  evaporation  ;  and  the  solid  bodies,  which 
are  thus  slowly  formed,  generally  assume  some  regular 
shape,  and  are  denominated  crystals.  As  the  fluid  is 
removed,  the  particles  come  gradually  into  the  sphere 
of  the  attractive  power  of  each  other,  and  thus  attain 
some  degree  of  cohesion  when  the  fluid  which  kept 
them  asunder  is  removed.  But  when  a  solid  is  ob- 
tained by  precipitation,  the  fluid  is  suddenly  removed 
from  between  the  particles,  which  are  consequently 
left  beyond  the  sphere  of  attraction  of  each  other,  and 
do  not,  therefore,  assume  any  regular  form.  And  thus 
it  will  follow  that,  the  more  slowly  the  process  of  evap- 
oration goes  on,  the  more  regular  will  be  the  crystals 
which  are  formed ;  and  this  corresponds  with  experi- 
ment and  observation. 


CHEMISTRY.  253 

Bodies  which  are  composed  of  particles  of  the  same 
nature  cohere  with  a  certain  force,  as  in  the  particles 
of  water  or  of  mercury,  and  those  of  wood  or  of  metal ; 
and  this  force  acts  with  different  degrees  of  intensity  : 
in  water  and  mercury,  it  is  comparatively  weak ;  but 
in  wood  and  metal,  it  is  very  powerful.  But  the  parti- 
cles of  dissimilar  bodies  also  enter  into  combination, 
and,  thus  united,  form  substances,  the  parts  of  which 
cohere  with  great  force  ;  and  whenever  these  com- 
binations take  place,  the  force  of  cohesion,  formerly 
subsisting  between  the  particles  of  each  of  the  bodies, 
must  be  destroyed  or  overcome,  before  the  new  com- 
bination can  take  place.  Thus  a  piece  of  marble  is 
dissolved  in  muriatic  acid ;  but  before  this  can  take 
place,  the  forc£  of  cohesion  which  existed  between  the 
particles  of  the  marble  must  be  overcome  ;  or,  in  other 
words,  the  force  of  attraction  between  the  particles  of 
the  muriatic  acid  and  the  particles  of  the  marble  must 
be  greater  than  that  between  the  particles  of  marble 
themselves.  This  attraction,  which  exists  between  the 
particles  of  substances  of  a  different  nature,  is  called 
chemical  affinity. 

This  attraction,  or  affinity,  does  not  exist  between  the 
particles  of  all  bodies.  Thus  there  is  no  affinity  be- 
tween marble  and  water,  as  there  is  between  marble 
and  muriatic  acid  :  water  has  not  strength  enough  to 
overcome  the  attraction  opposed  to  it ;  and  it  has  been 
thought  that  there  is  no  affinity  between  oil  and  water, 
because  the  particles  of  the  one  do  not  enter  into  com- 
bination with  those  of  the  other. 

Fourcroy  has  arranged  the  facts  which  depend  on 
chemical  affinity  under  ten  different  heads,  denomi- 
xiii.— 22 


55D4  CHEMISTRY. 

nated  the  laws  of  affinity.  These  may  be  considered  as 
chemical  axioms,  which  are  the  principles  or  founda- 
tions of  the  science.  They  are  as  follows  :  — 

1.  Chemical  affinity  takes  place  only  between  bodies 
of  a  different  nature. 

2.  Chemical  affinity  takes  place  only  between  the 
ultimate  particles  of  bodies. 

3.  Chemical  affinity   takes   place  between  several 
bodies. 

4.  In  order  that  chemical  affinity  may  take  place 
between  two  bodies,  it  is  necessary  that  one  of  them  be 
in  a  fluid  state. 

5.  When  bodies  combine  together,  they  undergo  a 
change  of  temperature. 

6.  The  compounds  formed  by  chemical  affinity  pos- 
sess new  properties,  and  different  from  those  of  their 
constituent  parts. 

7.  The  force  of  chemical  affinity  is  estimated  by 
the  force  which  is  required  to  separate  the  substances 
which  enter  into  combination. 

8.  Bodies  have  different  degrees  of  affinity  for  each 
other. 

9.  Affinity  is  in  the  inverse  ratio  of  saturation. 

10.  Between  two  compound  bodies,  which  are  not 
acted  upon  by  compound  affinities,  decomposition  may 
take  place,  if  the  affinity  of  a  compound,  consisting  of 
two  of  the  principles,  for  a  third,  be  greater  than  that 
which  unites  this  third  to  one  of  the  two  first,  or  to  the 
fourth  principle  —  although,  at  the  moment  of  action, 
the  union  between  the  first  two  does  not  exist. 

We  shall  now  proceed  to  describe  those  properties 
of  matter  which  are  strictly  chemical ;  but  a  part  of 


CHEMISTRY.  .  255 

this  work  has  been  anticipated  by  a  previous  chapter. 
Upon  these  properties,  numerous  classifications  have 
been  founded  ;  and  although  in  part  abandoned  at  the 
present  time,  in  favor  of  other  terms  more  rigidly 
chemical,  yet  we  so  frequently  use  the  words  airs, 
eartJis,  metals,  alkalies,  acids,  &c.,  that  it  will  be  proper 
briefly  to  enumerate  the  leading  characteristics  of  these 
substances. 

The  word  air  is  sometimes  employed  to  designate 
all  the  permanently  elastic  fluids,  and,  in  this  sense,  it  is 
synonymous  with  the  word  gas  ;  but  it  is  more  com- 
monly restricted  to  the  atmospheric  air  —  a  mixture 
principally  of  two  gases  —  in  which  we  live  and  breathe. 

The  term  eartJis  is  still  applied  to  one  class  of  sub- 
stances, though  rather  loosely ;  for  it  has  been  found 
that,  in  all  general  chemical  properties,  the  earths  and 
the  metallic  oxides  are  the  same,  and  nearly  all  the 
earths  have  metallic  bases.  Earths  have  been  de- 
scribed as  insipid ;  soluble,  but  in  very  small  proportion, 
in  pure  water  or  oil ;  not  inflammable,  not  ductile,  and 
not  fusible,  by  themselves ;  but  recently  the  powers  of 
the  Voltaic  pile,  and  the  gas  blowpipe,  have  shown  that 
they  are  fusible;  and  the  alkaline  earths  cannot  be 
termed  insipid. 

Of  the  metals  we  shall  speak  hereafter.  Their  two 
essential  chemical  properties  are,  the  power  of  con- 
ducting electricity,  and  the  possession  of  some  degree 
of  lustre.  They  are  all  capable  of  combining  with 
oxygen,  though  with  very  different  degrees  of  facility. 

The  alkalies  are  a  well-marked,  though  not  a  numer- 
ous, class  of  bodies.  The  term  alkali  is  derived  from 
the  Arabic  name  of  the  plant  from  which  one  of  these 


256  '        CHEMISTRY. 

substances  has  long  been  extracted.  The  general 
properties  of  the  alkalies,  especially  as  developed  in 
the  stronger  ones,  are  as  follows :  they  change  blue 
vegetable  colors  to  green ;  and  if  such  colors  have 
been  changed  to  purple,  or  to  a  more  vivid  red,  by 
acids,  they  destroy  that  sort  of  action,  and,  when  used 
in  sufficient  quantity,  turn  them  absolutely  green.  The 
same  power  they  possess  even  when  saturated  with 
carbonic  acid,  —  a  property  which  does  not  belong 
to  the  alkaline  earths.  Their  taste  is  acrid,  proba- 
bly arising,  in  a  great  degree,  from  their  power  of  dis- 
solving all  animal  matter  with  an  energy  proportioned 
to  their  state  of  concentration.  They  readily  combine 
with  oils  or  fatty  substances,  so  as  to  form  soaps. 
Their  carbonates  are  soluble  in  water,  but  the  carbon- 
ates of  the  alkaline  earths  are  not  so.  Three  of  the 
alkalines  consist  of  metallic  bases  united  with  oxygen, 
namely  potassa,  soda,  and  lithia.  One,  ammoniac,  con- 
sists of  two  gases,  hydrogen  and  nitrogen  ;  and  the 
vegetable  alkalies,  which  are  rather  numerous,  consist 
of  various  combinations  of  oxygen,  hydrogen,  and 
carbon. 

The  term  acid  is  in  familiar  use,  and  is  generally 
understood  by  all ;  its  chemical  sense  is,  in  fact, 
adopted  from  ordinary  language.  Acids  are  sub- 
stances having  a  sour  taste ;  they  are  frequently  highly 
corrosive  of  animal  and  vegetable  bodies,  and  they 
change  purple  vegetable  colors  to  a  brighter  red. 
Their  most  distinctive  chemical  property  is,  that  they 
unite  with  other  substances,  called  bases,  such  as  the 
alkalies,  the  earths,  and  metallic  oxides,  and  form  new 
classes  of  bodies,  called  salts,  in  which  the  antagonist 


CHEXISTKY.  257 

properties  of  both  acid  and  base  undergo  great  modifi- 
cations, or  are  absolutely  annihilated.  The  theory  of 
acidification  —  that  is,  the  effective  cause  of  producing 
acid  properties  —  has  not  yet  been  well  explained. 

In  a  chemical  sense,  substances  are  divided  into  two 
kinds,  simple  and  compound.  Simple  bodies  are  those 
which  have  not  been  separated  into  others  more  simple, 
nor  reproduced  by  artificial  means.  The  ancients  con- 
sidered four  substances  as  simple  and  uncompouuded, 
which  they  denominated  elements,  —  namely,/re,  air, 
earth,  and  water.  But  these  have  all  been  decom- 
posed, and  their  constituent  parts  well  ascertained. 
The  number  of  simple  substances  is  constantly  chan- 
ging, as  new  discoveries  are  made.  They  are  at 
present  divided  into  two  classes ;  the  one  called  com- 
bustible, or  inflammable,  and  the  other  supporters  of 
combustion  —  because,  in  combining  them  with  the  first 
class,  much  light  and  heat  are  developed.  Most  of  the 
simple  combustibles  have  been  proved  to  be  metals,  and 
hydrogen  is  believed  by  some  to  be  a  metal  in  an  elas- 
tic form. 

CALORIC,  or  heat,  is  a  most  important  agent  in  chem- 
istry. Its  general  tendency  is,  to  keep  the  particles  of 
matter  at  a  certain  degree  of  expansion.  It  pervades 
all  things,  but  some  in  a  greater  degree  than  others. 
Even  ice  has  been  found  to  contain  a  certain  portion  of 
heat  In  fact,  there  is  no  such  thing  in  nature  as  positive 
cold ;  the  things  that  seem  cold  to  us  are  only  under  a 
low  degree  of  heat.  The  absolute  nature  of  this  uni- 
versal principle  is  unknown ;  we  only  know  it  by  its 
effects  and  the  sensations  it  produces.  Some  have 
conjectured  that  it  is  a  fluid  ;  others  think  it  a  quality 
o.  22* 


258 


CHEMISTRY. 


or  affection  of  matter,  resulting  from  chemical  action. 
From  its  producing  no  sensible  difference  in  the  weight 
of  any  substance,  it  has  been  called  an  imponderable 
body.  When  the  heat  of  any  particular  substance,  as 
ice,  stone,  or  wood,  is  not  sensible  to  us,  it  is  called 
latent  or  concealed  heat.  We  may  very  readily  detect 
its  presence  in  a  piece  of  wood  or  metal  by  friction. 
If  a  button,  for  instance,  be  rubbed  on  a  table,  it  will 
soon  become  too  hot  to  be  held  by  the  fingers.  In  like 
manner,  the  axle  of  any  carriage-wheel  soon  becomes 
hot  unless  the  friction  is  prevented  by  grease. 

The  chemical  effects  of  heat  are  expansion,  lique- 
faction, vaporization,  evaporation,  and  ignition.  With 
few  exceptions,  bodies  are  capable  of  expansion  by 
means  of  heat ;  the  gases  being  the  most  expansive, 
fluids  less  so,  and  solids  least  of  all.  When  the  iron 
rim  of  a  coach  or  cart-wheel  is  to  be  put  on,  it  must 
first  be  heated  to  a  considerable  degree.  The  reason 
of  this  is  obvious  ;  when  hot,  the  circle  is  larger  than 
when  cold,  and  thus  slips  easily  on  the  wheel :  as  it 
cools,  the  circle  decreases,  and  thus  firmly  binds  the 
wood-work  together.  As  regards  fluid  bodies,  the 
same  fact  is  illustrated  in  the  case  of  the  thermometer 
and  barometer;  by  the  accession  or  loss  of  heat,  the 
mercury  expands  or  contracts  to  a  degree  indicated 
by  the  scale  annexed  to  the  instrument.  The  general 
law,  therefore,  is,  that  the  expansion  and  contraction  of 
matter  are,  with  a  few  exceptions,  dependent  upon  the 
increase  and  diminution  of  heat.  The  quantity  or  con- 
dition of  heat  that  is  discoverable  by  the  thermometer, 
or  by  the  organs  of  sensation,  is  called  temperature. 

Vaporization  is  the  rapid  production  of  a  thin  vapor 


CHEMISTRY.  259 

as  when  water  is  converted  into  steam.  The  boiling 
point  of  water,  in  a  vessel  exposed  to  the  ordinary 
atmospheric  pressure,  is  212  degrees  6f  Fahrenheit ; 
and,  although  more  heat  be  applied  to  the  vessel  in 
which  it  is  contained,  the  temperature  of  the  water  is 
not  increased.  If  this  degree  of  heat  be  continued, 
the  watery  particles  separate  from  each  other,  and 
become  steam  or  vapor.  Steam  is  colorless,  transpa- 
rent, and  invisible,  resembling  the  atmosphere  j  and 
is  1696  times  greater  in  bulk  than  its  weight  of  water. 
Steam  may  be  condensed,  or  its  particles  brought 
nearer  to  each  other,  either  by  removing  the  heat 
which  is  the  cause  of  the  vaporization,  or  by  mechanical 
pressure ;  and  the  result  is,  its  return  to  the  form  of 
water. 

Distillation  is  the  converting  of  a  liquid  into  vapor, 
which  is  afterwards  carried  off  through  a  pipe,  and 
condensed  in  what  is  called  a  refrigerator.  This  is  a 
vessel  filled  with  cold  water,  round  the  inside  of  which 
the  pipe  is  wound  ;  and  as  the  vapor  passes  through  the 
pipe,  it  is  condensed  by  the  lower  temperature  of  the 
water  within  the  vessel.  Liquid  substances  give  off 
vapor  from  their  surface  at  temperatures  below  the 
boiling  point,  which  is  termed  evaporation.  It  is  called 
spontaneous  evaporation  when  this  takes  place  at  the 
ordinary  temperature  of  the  atmosphere.  A  large 
quantity  of  vapor  is  given  off  from  the  surface  of  the 
earth  and  sea,  which  eventually  forms  clouds,  or  is 
condensed  into  rain  and  dew.  Evaporation  always 
produces  cold  when  heat  is  not  applied,  the  heat  neces- 
sary for  it  being  derived  from  the  surrounding  objects. 
A  current  of  air,  or  a  higher  temperature,  tends  greatly 


260  CHEMISTRY. 

to  quicken  evaporation,  as  may  be  observed  in  the 
rapidity  with  which  the  surface  of  the  earth  dries  when 
a  brisk  wind  passes  over  it. 

All  substances  become  luminous  when  heated  to 
800  degrees  in  the  dark,  and  1000  in  daylight,  unless 
they  are  converted  into  vapor  at  a  less  elevated  tem- 
perature. The  light  is  at  first  red,  and  in  this  state  the 
body  is  said  to  be  in  a  state  of  ignition.  If  more 
heat  ^s  applied,  the  body  becomes  white,  when  it  is 
said  to  be  incandescent.  When  a  body  changes  from 
the  solid  to  the  fluid  state,  a  quantity  of  heat  is  ab- 
sorbed which  has  no  effect  in  raising  the  temperature. 
This  is  called  latent  heat.  The  same  phenomenon  takes 
place  when  a  liquid  is  converted  into  vapor. 

COMBUSTION  is  a  process  not  yet  perfectly  under- 
stood. It  is  usually  described  as  the  union  of  a  com- 
bustible body  with  a  supporter  of  combustion,  attended 
with  the  evolution  of  light  and  heat.  The  combustible 
body  is  that  which  burns,  but  in  general  will  neither  sup- 
port combustion,  nor  burn,  except  in  presence  of  a  sup- 
porter of  combustion.  The  supporter,  again,  does  not  it- 
self burn,  though  necessary  to  the  burning  of  a  combusti- 
ble. Oxygen  gas,  the  ingredient  which  enables  the  air  to 
support  combustion,  possesses,  when  pure,  a  high  degree 
of  the  supporting  quality.  If  a  lighted  taper,  a  com- 
bustible body,  be  plunged  into  this  gas,  the  taper  burns 
vividly,  but  the  gas  itself  is  not  ignited.  If,  on  the 
other  hand,  the  taper  be  plunged  into  combustible  gas, 
such  as  pure  coal  gas,  the  gas  is  instantly  ignited,  but 
the  taper  is  extinguished.  By  examining  the  effects 
of  combustion  in  the  case  of  a  candle  burning  in 
the  atmosphere,  it  has  been  proved,  pretty  clearly, 


CHEMISTRY.  261 

that  a  chemical  action  of  the  following  kind  takes 
place  :  The  combustible  matter  of  the  candle  consists 
chiefly  of  two  simple  bodies,  hydrogen  gas  and  carbon, 
while  oxygen  is  the  supporter  of  combustion  in  the  air. 
On  burning  a  candle  under  a  bell-shaped  glass,  filled 
with  common  air,  a  fluid  gathers  on  the  glass,  which 
proves,  on  examination,  to  be  pure  water.  The  hydro- 
gen of  the  burning  body  has  here  entered  into  combina- 
tion with  part  of  the  oxygen  of  the  air,  forming  water, 
a  compound  of  the  two.  The  carbon  of  the  burning 
body  also  enters  into  union  with  a  portion  of  the  atmos- 
pheric oxygen,  forming  carbonic  acid  gas,  which  is 
left  floating  in  place  of  the  original  quantity  of  oxygen. 
The  same  process  takes  place  in  the  burning  of  coal, 
&c.  Thus  it  seems  that  combustion  only  changes  the 
forms  of  the  burned  bodies,  and  does  not  annihilate 
them. 

AIB,  by  the  examinations  of  modern  chemists,  has 
been  shown  to  be,  not  an  element  or  a  simple  sub- 
stance, but  a  compound  body,  consisting  chiefly  of  two 
gases,  oxygen  and  nitrogen.  It  also  appears  that  the 
oxygen  is  the  really  active  agent,  in  relation  to  animal 
respiration,  and  that  the  nitrogen  is  a  mere  diluent,  in 
the  mass,  on  the  same  principle  as  water  may  be  made 
a  diluent  of  spirits.  Each  individual  is  supposed,  on  an 
average,,  to  breathe  about  twenty  times  in  a  minute ;  to 
take  in  about  sixteen  cubic  inches  of  air  at  each  in- 
spiration ;  to  return  nearly  the  whole  of  the  nitrogen 
and  four  fifths  of  the  oxygen ;  and  to  replace  the  re- 
maining fifth  of  oxygen  by  an  equal  volume  of  car- 
bonic acid  gas.  The  oxygen  of  the  air  is  the  great 


262  CHEMISTRY. 

means  of  procuring  heat  and  light,  by  its  action  with 
combustible  bodies. 

WATER  was  also,  at  one  period,  believed  to  be  a  sim- 
ple element  in  nature  ;  but  this  supposition  has  given 
way  before  the  examinations  of  chemists.  Water  is 
now  known  to  be  composed  of  oxygen  and  hydiogen 
gas,  in  the  proportions  of  8  of  the  former  to  1  of  the 
latter.  Into  these  substances  it  can  be  resolved,  by  the 
action  of  electricity  or  fire.  Sea-water  contains,  in 
1000  parts,  about  46  of  foreign  matters,  chiefly  chlo- 
ride of  sodium.  Mineral  waters,  in  a  similar  manner, 
contain  various  foreign  bodies  —  as,  for  example,  car- 
bonated waters,  which  contain  carbonic  acid  ;  sulphu 
reous  waters,  which  hold  sulphureted  hydrogen;  and 
chalybeate  waters,  which  contain  sulphate  or  carbonate 
of  iron.  When  water  contains  a  chemical  compound 
of  lime,  it  is  said  to  be  hard  ;  and,  in  this  state,  it  de- 
composes the  soap  which  is  employed  with  it. 

NITROGEN,  or  azote,  is  a  gas  permanently  elastic, 
transparent,  colorless,  and  inodorous.  It  is  very  little 
lighter  than  oxygen.  When  breathed,  it  destroys  ani- 
mal life  ;  and  a  burning  body,  if  immersed  in  a  jar  con- 
taining it,  is  instantly  extinguished.  United  with  ox- 
ygen in  one  proportion,  it  forms  nitric  acid,  or  aqua- 
fortis. Another  compound  of  these  two  materials,  in 
different  proportions,  constitutes  the  protoxide  of  azote, 
or,  as  it  was  formerly  called,  nitrous  oxide,  the  inhala- 
tion of  which  causes  a  sort  of  temporary  intoxication. 

OXYGEN  is  a  permanently  elastic  fluid,  colorless,  and 
destitute  of  taste  or  smell :  combustible  bodies  burn  in 
it  with  more  brilliancy,  and  more  light  and  heat  are 


CHEMISTRY.  ZO3 

evolved,  than  when  combustion  takes  place  in  the  at- 
mosphere. HYDROGEN  is  also  a  permanently  elastic 
fluid.  It  is  the  lightest  body  with  which  we  are  ac- 
quainted, and  is  employed,  in  combination  with  other 
gases,  to  inflate  balloons.  A  bladder  filled  with  this  gas 
will  ascend  in  the  atmosphere  in  the  same  manner 
as  a  piece  of  cork  plunged,  to  the  bottom,  will  rise  in 
water. 

CHLORINE  is  a  gaseous  body  of  a  yellowish  green 
color,  a  strong,  suffocating  smell,  and  a  very  astringent 
taste.  If  breathed  undiluted,  it  destroys  animal  life  ; 
yet  it  not  only  supports  combustion,  but  possesses  the 
remarkable  quality  of  setting  fire  to  many  of  the 
metals,  even  at  the  common  temperature  of  the  air, 
when  they  are  beaten  out  into  thin  leaves  and  intro- 
duced into  it.  The  combinations  of  metals  with  chlorine 
are  called  chlorides.  Chlorine  possesses  the  property 
of  destroying  all  vegetable  colors,  and  of  rendering 
vegetable  bodies  exposed  to  its  action  white.  This 
property  renders  it  useful  in  bleaching :  combined  with 
hydrogen,  it  forms  muriatic  acid,  which,  united  with 
oxides,  produces  an  immense  number  of  salts,  such  as 
common  sea-salt,  which  is  a  muriate  of  soda. 

CARBON,  or  charcoal,  is  found  in  many  different 
forms,  and  can  be  prepared  by  burning  wood,  &c.,  in 
close  vessels.  The  diamond  is  pure  carbon ;  and 
plumbago,  or  black  lead,  is  principally  composed  of 
this  substance  united  with  a  little  iron.  It  combines 
with  all  the  supporters  of  combustion,  and,  with  oxygen, 
forms  carbonic  acid.  SULPHUR,  or  brimstone,  we  shall 
describe  hereafter  in  the  chapter  upon  minerals.  When 
heated  to  170  degrees,  it  becomes  volatilized,  and  the 


264  CHEMISTRY. 

result  is  a  fine  powder  denominated  powers  of  sulphur. 
Combined  with  oxygen,  it  forms  sulphuric  acid,  or  oil 
of  vitriol. 

PHOSPHORUS  is  chiefly  prepared  from  bones,  which 
consist  mostly  of  the  phosphate  of  lime.  It  is  an  arn- 
ber-colored  and  semi-transparent  solid,  so  very  com- 
bustible that  it  takes  fire  in  the  air,  emitting  a  white 
smoke  having  a  smell  of  garlic.  It  also  appears  lumi- 
nous in  the  dark. 

Such  is  a  brief  description  of  some  of  the  most  im- 
portant of  the  simple  or  elementary  bodies  which  com- 
pose all  known  substances.  Others  we  shall  hereafter 
notice  in  the  article  on  minerals.  In  a  general  sum- 
mary, we  may  state  that  the  simple  bodies,  or  those 
which  have  never  been  decomposed,  are  fifty-four  in 
number ;  and,  for  the  convenience  of  study,  they  have 
been  divided  into  metallic  and  non-metallic  substances. 
The  non-metallic  elements  are  again  divided  into 
gazolytes,  or  bodies  which  are  permanently  gaseous ; 
metalloids,  or  bodies  which  resemble  the  metals  in 
their  chemical  relations ;  and  halogens,  or  bodies  which 
produce  salts  when  in  union  with  the  metals.  The  non- 
metallic  elements  are  thirteen  in  number,  —  namely, 
oxygen,  hydrogen,  nitrogen,  chlorine,  iodine,  bromine, 
fluorine,  boron,  carbon,  silicon,  sulphur,  selenium,  and 
phosphorus.  The  first  three  are  the  gazolytes,  the 
next  four  the  halogens,  and  the  remaining  six  the  met- 
alloids. The  metallic  elements  are  forty-one  in  num- 
ber,—  namely,  potassium,  sodium,  lithium,  calcium, 
borium,  strontium,  magnesium,  aluminum,  thorium, 
glucium,  zirconium,  yttrium,  manganese,  zinc,  iron, 
tin,  cadmium,  cobalt,  nickel,  arsenic,  chromium,  vana- 


eHE.MISTRY.  265 

dium,  molybdenum,  tungsten,  columbium,  antimony, 
uranium,  cerium,  bismuth,  titanium,  tellurium,  copper, 
lead,  mercury,  silver,  gold,  platina,  palladium,  rhodium, 
osmium,  and  iridium.  These  metallic  elements  are 
again  divided  into  three  orders, — the  first  twelve  being 
(he  bases  of  the  alkalies  and  earths  ;  the  next  twenty- 
one  being  metals  whose  oxides  are  not  reduced  by 
heat  alone,  and  the  remaining  eight,  whose  oxides  are 
reduced  by  a  red  heat. 

From  these  fifty-four  elementary  substances  are 
formed  all  the  beautiful  varieties  of  terrestrial  objects  : 
nor  is  there  any  thing  very  wonderful  or  mvsterious  in 
this  fact ;  since,  as  we  have  seen,  any  given  two  of  them, 
if  made  to  unite  in  different  proportions,  are  capable 
of  producing  the  most  opposite  substances.  Thus  nitro- 
gen and  hydrogen,  combined  in  certain  proportions, 
form  the  vital  air  which  we  breathe  ;  the  same  ele- 
ments, combined  in  another  proportion,  produce  an  in- 
toxicating gas  ;  and  again,  in  still  another,  produce  aqua- 
fortis, which  is  a  deadly  poison.  It  is  also  to  be  ob- 
served that  new  substances,  thus  produced,  united  with 
each  other,  give  rise  to  new  compounds,  which  are 
susceptible  of  being  combined,  and  so  on  through  an 
almost  infinite  diversity  of  chemical  union.  From 
recent  experiments  in  chemistry,  however,  it  has 
been  suggested  that  all  substances  whatever  are  but 
modifications  of  one  primitive  element ;  but  the  abso- 
lute truth  of  this  startling  theory  remains  to  be  practi- 
cally demonstrated. 


xra. — 23 


GEOLOGY.* 


THIS  science  proposes  to  investigate  the  natural 
history  of  the  earth  —  especially  the  general  structure 
of  what  may  be  called  its  crust.,  or  shell.  It  does  not 
entirely  overlook  the  internal  strata,  or  even  the 
nucleus,  of  our  globe;  but  as  these  are  beyond  our 
inspection,  it  is  possible  to  offer  little  more  than  spec- 
ulations respecting  them. 

This  noble  science  is  of  modern  date.  Certain 
theories  had,  indeed,  been  offered  upon  this  subject; 

*  For  a  full  view  of  this  subject,  see  "  Wonders  of  Geology." 


GEOLOGY.  267 

but  the  extravagance  of  these,  proceeding,  as  they  often 
did,  from  men  of  the  highest  talent,  affords  humiliating 
lessons  as  to  the  absurdities  in  which  the  master-spirits 
of  our  race  may  be  involved,  when  their  footsteps  do 
not  follow  the  paths  of  experiment  and  observation. 
The  great  mathematician  Kepler  attempted  to  prove 
that  the  earth  was  a  vast  animal ;  the  tides  he  re- 
garded as  occasioned  by  the  heavings  of  its  prodigious 
lungs.  I  .a'o  and  the  Stoics  seem  to  have  entertained  a 
similar  opinion.  Whiston,  the  English  divine,  consid- 
ered the  earth  as  produced  by  the  condensation  of  a 
comet,  and  the  deluge  as  occasioned  by  the  visit  of 
one  of  those  erratic  orbs. 

Other  theorists  have  ascribed  the  origin  of  the  globe 
to  fragments  which  have  fallen  successively  from  the 
heavens,  in  the  form  of  aerolites.  Our  own  Captain 
Symmes,  of  Cincinnati,  seriously  maintained  that  the 
earth  was  hollow,  and  inhabited,  and  that  the  interior 
was  accessible  by  openings  at  the  poles.  He  brought 
a  vast  deal  of  learning  to  the  support  of  his  theory, 
and  even  undertook  to  equip  an  expedition  for  the  pur- 
pose of  exploring  the  polar  regions,  in  order  to  deter- 
mine the  question  by  observation.  Perhaps,  however, 
the  palm  of  absurdity  must  be  awarded  to  Voltaire,  who 
accounted  for  the  immense  masses  of  sea-shells,  found 
upon  the  mountains  of  Geneva,  by  supposing  them  to 
have  been  thrown  there  from  the  wallets  of  pilgrims 
in  the  holy  wars !  Such  are  some  of  the  follies  into 
which  the  highest  intellect  may  be  led,  either  by  a  par- 
tial observation  of  facts,  or  the  adoption  of  a  false 
philosophy. 

The  application  of  Lord  Bacon's  rule,  which  instructs 


268  GEOLOGY. 

us  to  collect  facts  first,  and  form  theories  afterwards, 
has  exploded  the  vain  speculations  of  former  geologists 
and  resulted  in  the  establishment  of  the  modern  science 
upon  a  permanent  and  secure  basis.  The  first  person 
who  pointed  out  the  proper  mode  of  investigation,  in 
the  pursuit  of  geological  knowledge,  was  William 
Smith,  a  land  surveyor,  of  Bath,  England,  who,  in 
constructing  roads  and  canals,  observed  that  the  same 
strata  gave  the  same  fossils,  and  that  strata  and  fossils 
were  always  identical.  This  was  a  key  ;  and  no  study 
ever  became  more  popular,  and  raised  itself  into  uni- 
versal estimation  more  suddenly.  Parkinson,  Cuvier, 
Mantell,  Brogniart,  Sedgwick,  Buckland,  Murchison, 
Greenough,  Lyell,  Philips,  Silliman,  and  the  learned 
societies  throughout  Christendom,  have  been  active  in 
exploring  this  interesting  field  of  knowledge. 

NATURE  OF  THE  CRUST  OF  THE  EARTH. 

The  greatest  thickness  of  the  superficial  crust  of  the 
globe  —  that  is,  of  the  mass  of  solid  materials  which  the 
ingenuity  of  man  has  been  able  to  examine,  from  the 
highest  mountain-peaks  to  the  greatest  natural  or  arti- 
ficial depths  —  is  estimated  at  about  10  miles.  As  the 
earth  is  nearly  8000  miles  in  diameter,  the  entire  series 
of  strata  hitherto  explored  is,  therefore,  but  very  insig- 
nificant, compared  with  the  magnitude  of  the  globe; 
bearing  about  the  same  relative  proportion  as  the 
thickness  of  paper  to  an  artificial  sphere  a  foot  in 
diameter ;  the  inequalities  and  crevices  in  the  varnish 
of  such  an  instrument  would  be  equal,  in  proportionate 
size,  to  the  highest  mountains  and  deepest  valleys. 

As  a  thickness  of  100  miles  so  far  exceeds  that  of 


the  whole  of  the  strata  that  are  accessible  to  human 
observation,  we  cannot  doubt  that  disturbances  of  the 
earth's  surface,  even  to  ten  times  the  depth  of  those 
which  come  within  the  scope  of  geological  inquiry, 
may  take  place,  without  in  any  degree  affecting  the 
entire  mass  of  the  globe.  If  these  facts  be  duly  con- 
sidered, the  mind  will  be  prepared  to  receive  one  of 
the  most  startling  propositions  in  modern  geology  — 
namely,  that  the  highest  mountains  have  once  been  the 
bed  of  the  sea,  and  have  been  raised  to  their  present 
situations  by  subterranean  agency, — some  slowly, 
others  suddenly ;  but  all,  geologically  speaking,  at  a 
comparatively  recent  period. 

The  superficial  crust  of  the  globe  is  composed  of 
numerous  layers  and  masses  of  earthy  substances,  of 
which,  combinations  of  iron,  lime,  and  silex,  or  flint, 
constitute  a  large  proportion ;  the  latter  forming  45  per 
cent,  of  the  whole.  Those  strata  which  have  been  de- 
posited the  latest,  bear  evident  marks  of  mechanical 
origin,  and  are  the  water-worn  rubs  of  older  rocks ; 
as  we  descend,  materials  of  a  denser  character  appear, 
which  also  exhibit  proofs  of  having  been  subject  to  the 
action  of  water ;  but  when  we  arrive  at  the  lowermost 
in  the  scale,  a  crystalline  structure  generally  prevails ; 
and  while,  in  the  newer  strata,  trees,  plants,  shells,  and 
other  remains  of  animals  and  vegetables,  are  found  in 
profusion,  in  the  most  ancient  rocks  all  traces  of 
organic  forms  are  absent 

CLASSIFICATION  OF  ROCKS. 

In  casting  a  casual  glance  over  the  broken  and  diver- 
sified surface  of  the  globe,  its  materials  might  present 
23* 


270  GEOLOGY. 

a  scene  of  utter  confusion  ;  but  the  scientific  observer 
by  investigation  and  comparison,  is  able  to  make  out 
certain  analogies  which  become  the  foundation  of  sci- 
entific arrangement.  Thus  geologists  class  all  the 
rocks  which  form  the  crust  of  our  globe  into  two 
grand  divisions  —  viz.,  the  unstratifad  and  the  strati' 
fad.  The  former  are  supposed  to  have  been  formed 
by  the  action  of  fire,  and  have,  therefore,  been  called 
igneous.  These  are  entirely  destitute  df  organic  re- 
mains. The  latter  are  disposed  in  beds  or  strata,  and, 
being  supposed  to  derive  their  present  arrangement 
from  the  action  of  water,  are  called  aqueous.  Among 
these  are  found  the  fossil  remains  of  plants  and  ani- 
mals. The  igneous  or  unstratified  rocks  form  an 
extensive  group,  of  which  granite  and  lavas  occupy  a 
prominent  part.  Porphyry,  diallage,  pitchstone,  basalt, 
scoriae,  and  the  trap-rocks,  belong  to  the  same  series. 
All  these  substances  possess  evidences  of  a  common 
origin,  and  exhibit  the  same  geological  phenomena. 
Their  relative  ages,  in  respect  to  each  other,  we  have 
no  means  of  determining.  But  there  are  certain  rules 
by  which  we  may  ascertain,  in  particular  circumstances, 
their  relative  antiquity,  as  compared  with  adjacent 
'ocks.  For  example,  if  we  find  a  mass  of  granite 
penetrating  a  particular  stratum,  breaking  it  up,  and 
branching  through  it  in  veins,  we  must  conclude  that 
here  the  granite  is  the  more  recent  of  the  two ;  that 
it  assumed  its  present  position  subsequently  to  the  for- 
mation of  the  stratum  which  it  traverses. 

The  figure  at  p.  272  represents  granitic  veins,  branch- 
ing through  stratified  rocks,  and  overlaying  them  at  the 
surface.  The  proofs  of  the  igneous  origin  of  the  un- 


271 


272 


Granitic  Veins  p 


through  Strata. 


stratified  rocks  are  very  complete :  not  only  does  their 
structure  establish  it,  but  we  find  that,  wherever  they 
have  been  erupted  into,  or  through,  the  stratified  rocks, 
the  texture  of  the  latter,  at  the  point  of  contact,  ex- 
hibits the  marks  of  the  action  of  intense  heat.  Thus, 
wherever  the  slate-rocks  are  intersected  by  granitic 
veins,  they  assume  the  appearance  of  mica-slate,  or 
hornblende ;  beds  of  shale  and  sandstone  are  reduced 
to  jasper,  and  compact  limestone  and  chalk  are  con- 
verted into  crystalline  marble. 

The  stratified  rocks  have  been  classed  under  the  four 
following  divisions :  — 

1.  The  primary ,  consisting  of  gneiss,  quartz,  horn- 
blende, &c.,  but  containing  no  organic  remains. 

2.  The   transition,  presenting  alternations  of  slate 
and  shale,  with  slaty  sandstone,  limestone,  and  con- 
glomerate  rocks,   and   containing   remains   of  fishes, 
shells,  and  vegetables.     The  coal-formation  belongs  to 
this  division. 

3.  The  secondary,  which  include  the  lias  and  oolite 
formations,  various  limestones,  variegated  sandstone, 


GEOLOGY.  273 

conglomerates,  and  others.  They  are  richer  in  organic 
remains  than  the  transition  rocks.  We  here  find  the 
remains  of  gigantic  lizards,  of  the  most  extraordinary 
description,  with  turtles,  opossums,  and  kangaroos,  and 
various  kinds  of  trees  and  plants. 

4.  The  tertiary  rocks,  consisting  chiefly  of  alterna- 
ting strata  of  marine  and  fresh-water  deposits,  and 
containing  in  great  abundance  the  remains  of  animals 
and  plants,  approaching,  in  genus  or  species,  to  those 
which  at  present  inhabit  our  continents  and  seas. 

ARRANGEMENT  OF  STRATA. 

The  igneous  and  primary  rocks  constitute,  mainly, 
the  hills  of  New  England,  and  the  mountain  group  in 
the  northern  part  of  New  York;. also  the  Blue  Ridge 
and  its  collateral  elevations,  extending  south-westerly 
through  the  Atlantic  states.  The  transition  and  sec- 
ondary rocks  constitute  the  greatest  portion  of  the  inte- 
rior of  the  United  States,  west  of  New  England.  The 
tertiary  deposits  form  a  large  portion  of  the  shores  and 
low  country  of  the  states  south  of  New  England,  and 
bordering  on  the  Gulf  of  Mexico. 

Strata  are  generally  inclined  at  greater  or  less 
angles  to  the  horizon  ;  and  their  ends  or  edges  crop  out, 
at  the  surface,  from  under  each  other:  were  the  ar- 
rangement othenvise,  we  should  have  remained  forever 
in  ignorance  of  many  of  the  lower  rocks,  because  we 
could  only  have  reached  them  by  cutting  through 
enormous  superincumbent  masses,  of  impenetrable 
thickness ;  coal,  for  example,  would  have  been  un- 
known to  us,  and  also  the  metals  in  which  the  inferior 


274 


Strata  cropping  out. 

strata  abound.  But,  in  consequence  of  the  admirable 
arrangement  of  nature,  we  obtain  easy  access  to  all 
the  different  districts. 

As  we  walk  over  a  country,  we  perhaps  come  upon 
the  out-crop  of  primitive  rocks;  and  here,  though 
dreary  and  barren,  the  country  is  wild  and  romantic, 
and  affords  valuable  minerals.  We  advance  upon  more 
recent  formations,  where  we  have  no  minerals,  but 
where  we  find  a  district  rich  in  agricultural  produce. 
Farther  on,  it  may  be,  we  come  to  strata  abounding 
in  coal,  and  affording  scope  for  the  exercise  of  manu- 
facturing industry. 

Strata  are  not  only  elevated  at  various  angles,  but 
we  often  find  them  twisted  and  contorted  in  divers 
forms,  according  as  they  have  been  acted  upon  by  the 
igneous  agents  which  disturbed  their  original  tran- 
quillity. 

AGE  OF  ROCKS. 

The  relative  antiquity  of  stratified  rocks  is  deter- 
mined by  the  order  in  which  they  lie  upon  each  other, 
and  by  the  organic  remains  of  animals  and  plants  im- 
bedded in  them.  Thus  the  aqueous  deposits  of  the 
present  period,  those  which  we  see  forming  under  our 


GEOLOGY.  275 

own  eyes,  and  which  enclose  the  remains  of  vegetables 
scarcely  altered,  and  of  animals  still  living  on  the  sur- 
face of  the  globe,  are  the  uppermost  of  all  the  others. 
Immediately  below  these  comes  the  diluvium,  of  the 
nature  of  which  little  is  known.  Continuing  to  descend, 
we  meet  with  rocks,  the  remains  enclosed  in  which  differ, 
more  and  more,  from  those  of  our  day.  At  last,  we 
arrive  at  the  crystalline  stratified  groups ;  the  oldest  of 
two  rocks  being  always  that  which  is  lowest  These 
different  group,  again,  are  subdivided  into  formations ; 
and,  independently  of  superposition,  we  judge  of  their 
relative  ages,  and  of  the  length  of  time  which  must  have 
elapsed  between  them,  by  the  fossils  peculiar  to  each. 

Let  us  take  the  tertiary  rocks,  for  example.  This 
auUBB  has  been  arranged  under  four  chronological  di- 
visions. In  the  oldest,  out  of  1200  shells  found  in  the 
strata,  not  50  belong  to  existing  species.  In  the 
second,  out  of  1000,  we  have  about  170  still  surviv- 
ing. In  the  next,  from  a  half  to  a  third  of  the 
shells  now  exist ;  and  in  the  fourth,  or  more  recent, 
almost  all  the  imbedded  shells  belong  to  species  still 
living  in  our  seas.  In  Sicily,  portions  of  the  last-men- 
tioned, or  newest  formations,  rise  to  the  height  of  2000 
feet,  and  contain  shells  and  corals  which  are  at  present 
found  in  the  Mediterranean. 

FORMATION  OF  ROCKS  AM)  STRATA. 
Among  the  recent  formations,  peat  is  one  of  the 
most  curious.  It  is  formed  of  decomposed  vegetables, 
and  is  supposed  to  be  the  origin  of  coal.  Forests 
which  have  been  overthrown  by  storms,  instances  of 
which  have  been  frequent,  contribute  to  the  formation 


276  GEOLOGY. 

of  peat.  The  decay  of  the  leaves  and  small  branches 
commences  the  process,  and  the  interstices  are  gradually 
filled  up,  until  the  trunks  are  enclosed  and  covered. 
Hence  the  frequent  occurrence  of  the  remains  of 
trees,  both  in  the  peat  and  coal  formations.  These 
trees  are  sometimes  so  numerous  as  to  form,  in  fact, 
fossil  forests.  In  the  valley  of  the  Saome,  a  mass 
of  peat  reposes  on  an  immense  quantity  of  the  branches 
and  trunks  of  the  dycotylenous  trees  heaped  on  each 
other,  and  resting  on  clay.  On  the  "borders  of  the 
Rhine,  there  exist  similar  masses,  in  which  the  trunks 
are  so  flattened,  that  trees  of  a  foot  in  diameter  present 
a  thickness  of  only  two  inches. 

Of  the  vegetable  origin  of  coal  there  can  be  no 
question.  In  order  to  account  for  the  formation  of  the 
immense  beds  of  this  useful  mineral  which  are  found, 
we  may  suppose  that  vast  masses  of  peat  have  been 
formed  by  a  vigorous  and  luxuriant  vegetation,  created 
by  heat  and  moisture.  These,  by  some  convulsions  of 
the  surface  of  the  earth,  have  been  sunk  beneath 
superincumbent  layers  of  earth  or  water,  and  thus  sub- 
jected to  great  pressure.  In  this  position,  in  the  course 
of  ages,  and  probably  by  the  aid  of  great  heat,  they 
have  been  converted  into  beds  of  coal.  These  are 
found  in  all  climates  —  in  India,  Europe,  America, 
New  Holland,  and  Greenland. 

Various  beds  of  sandstone  are  found  to  exist  amid 
the  stratified  rocks.  These  have  been  produced  by 
the  decomposition  of  older  rocks.  The  evidences  of 
this  are  abundant.  The  old  red  sandstone,  for  exam- 
ple, is  composed  of  quartz,  feldspar,  and  mica.  In  the 
more  recent  sandstone,  fossil  remains  of  trees  and 


GEOLOGY.  277 

plants  are  very  common.  The  interior  of  the  plant 
is  usually  filled  up  with  sand,  while  the  bark  is  con- 
verted into  coal.  Shells,  encrinites,  and  other  fossils, 
are  also  found  in  this  formation.  The  new  red  sand- 
stone is  found  in  New  Jersey,  and  along  the  banks  of 
Connecticut  River,  and  constitutes  a  building  material 
much  in  use. 

Limestone  formation  composes  nearly  one  eighth 
part  of  the  crust  of  the  globe.  The  recent  limestone  is 
produced  partly  by  the  secretions  of  shells  and  coral- 
lines, and  partly  from  the  decomposition  of  ancient 
limestone  rock.  Whence  the  latter  has  been  derived 
is  not  yet  determined,  though  it  is  probable  that  this 
also  is  formed  of  coral,  shells,  and  other  marine  sub- 
stances. The  mountain  limestone  contains  many 
crevices,  and  sometimes  vast  caverns  hung  with  sta- 
lactites, which,  seen  by  torchlight,  present  spectacles  ri- 
valling the  scenes  presented  in  the  tales  of  enchantment. 

Coral  reefs  are  among  the  most  interesting  phenom- 
ena in  geology.  Vast  islands  in  the  midst  of  the 
ocean,  reaching  to  the  bottom  of  the  almost  fathomless 
deep,  and  spreading  out  for  hundreds  of  miles  upon  the 
surface,  belong  to  this  class ;  but  the  most  curious  cir- 
cumstance is,  that  they  are  the  production  of  animal- 
cules scarcely  visible  to  the  naked  eye.  It  is  wonder- 
ful to  reflect  that  the  structures  of  these  minute  crea- 
tures surpass  in  magnitude,  by  a  thousand  fold,  all  the 
works  of  mankind  from  the  creation  to  the  present  day. 
The  manner  in  which  the  corallines  work  is  curious, 
and  seems  to  evince  something  that  approaches  intelli- 
gence. Having  once  raised  their  structure  above  the 
water,  so  as  to  serve  for  a  wall,  to  breast  the  waves 
xm — 24 


278  GEOLOGY. 

they  proceed  to  the  leeward  side,  where  they  can  work 
in  quiet,  undisturbed  by  the  agitation  of  the  sea. 

When  the  mass  has  been  formed  to  some  extent,  the 
action  of  water  and  the  atmosphere  decomposes  the 
surface,  and  furnishes  an  alluvial  soil.  Seeds  of 
plants  are  borne  thither  by  the  waters  and  the  wind, 
and  vegetation  begins.  Birds  resort  to  it ;  the  eggs  of 
insects  are  carried  thither ;  and  man,  at  last,  comes  and 
forms  a  settlement :  such  is  the  history  of  most  islands. 
Some  of  them,  disturbed  by  volcanic  action,  present 
peaks  and  cliffs  200  or  300  feet  in  height.  The  won- 
derful labors  of  the  zoophites  have  been  commemo- 
rated in  the  following  lines  by  Mrs.  Sigourney :  — 

Toil  on  !  toil  on  !  ye  ephemeral  train, 

Who  build  in  the  tossing  and  treacherous  main ; 

Toil  on  ;  —  for  the  wisdom  of  man  ye  mock, 

With  your  sand-based  structures  and  domes  of  rock  • 

Your  columns  the  fathomless  fountains  lave, 

And  your  arches  spring  up  to  the  crested  wave ; 

Ye're  a  puny  race,  thus  boldly  to  rear 

A  fabric  so  vast,  in  a  realm  so  drear. 

Ye  bind  the  deep  with  your  secret  zone ; 
The  ocean  is  sealed,  and  the  surge  a  stone ; 
Fresh  wreaths  from  the  coral  pavement  spring, 
Like  the  terraced  pride  of  Assyria's  king ; 
The  turf  looks  green,  where  the  breakers  rolled  ; 
O'er  the  whirlpool  ripens  the  rind  of  gold ; 
The  sea-snatched  isle  is  the  home  of  men, 
And  mountains  exult  where  the  wave  hath  been 

But  why  do  ye  plant,  'neath  the  billows  dark, 
The  wrecking  reef  for  the  gallant  bark  ? 
There  are  snares  enough  on  the  tented  field  : 
'Mid  the  blossomed  sweets  that  the  valleys  yield, 


GEOLOGY.  279 

There  are  serpents  to  coil  ere  the  flowers  are  up  • 
There's  a  poison-drep  in  man's  purest  cup  : 
There  are  foes  that  watch  for  his  cradle  breath,  — 
And  why  need  je  sow  the  floods  with  death  ? 

With  mouldering  bones  the  deeps  are  white, 
From  the  ice-clad  pole  to  the  tropics  bright ; 
The  mermaid  hath  twisted  her  fingers  cold 
With  the  mesh  of  the  sea-boy's  curls  of  gold, 
And  the  gods  of  the  ocean  have  frowned  to  see 
The  mariner's  bed  in  their  halls  of  glee. 
Hath  earth  no  graves,  that  ye  must  spread 
The  boundless  sea  for  the  thronging  dead  ? 

Ye  build  —  ye  build  —  but  ye  enter  not  in, 

Like  the  tribe  whom  the  desert  devoured  in  their  sin . 

From  the  land  of  promise,  ye  fade  and  die 

Ere  its  verdure  gleams  forth  on  your  weary  eye; 

As  the  kings  of  the  cloud-crowned  pyramid,  — 

Their  noteless  bones  in  oblivion  hid,  — 

Ye  slumber  unwaked  'mid  the  desolate  main, 

While  the  wonder  and  pride  of  your  works  remain. 

Chalk,  which  is  found  in  vast  beds,  appears  to  have 
been  entirely  composed  of  masses  of  marine  shells 
gradually  consolidated,  with  a  little  intermixture  of 
foreign  matter.  It  is  common  in  England  and  France, 
but  none  has  yet  been  found  in  America.  Rock-salt  is 
an  extensive  formation,  but  its  origin  has  not  been  sat- 
isfactorily explained.  The  strata,  both  above  and 
below  it,  have  been  found  to  contain  organic  remains. 

Diluvium  consists  of  those  beds  of  gravel,  clay,  and 
sand,  which  we  find  on  the  surface  of  the  upper  strata. 
They  are  not  usually  stratified,  and  contain  immense 
numbers  of  rounded  stones,  some  of  great  size  and 
weight.  These  comprehend  specimens  of  various 


280  GEOLOGY. 

rocks,  such  as  mica-slate,  granite,  trap,  sandstone, 
ironstone,  and  many  others.  These  have  evidently 
been  subjected  to  the  action  of  water,  by  which  they 
have  been  rolled  against  each  other  till  they  have  as- 
sumea  their  present  smooth  and  rounded  appearance. 
They  are  often  found  in  elevated  situations,  having 
been  brought  hither  by  vast  currents  of  water  in  some 
convulsion  of  nature  which  upheaved  the  surface  of 
the  earth. 

Alluvial  soil  is  to  be  distinguished  from  diluvium ; 
the  former  consisting  of  those  recent  masses  of  earth 
which  are  carried  down  by  rains  and  floods,  and  depos- 
ited in  valleys  along  the  banks  of  lakes  and  rivers. 

Erratic  blocks,  or  boulders,  are  those  enormous 
masses  of  granite,  and  other  stones,  which  are  found 
often  at  a  great  distance  from  any  beds  of  similar  for- 
mation. They  lie  scattered  over  the  plains,  and  even 
on  the  elevated  sites  of  mountains,  in  many  countries. 
It  would  appear  that  some  of  these,  weighing  many 
tons,  have  been  torn  from  their  original  resting- 
place,  and  carried  to  a  distance  of  hundreds  of  miles. 
Similar  blocks  of  granite  have  been  found  in  Iceland, 
which  is  entirely  composed  of  lava  ;  and  the  nearest 
point  from  which  they  have  been  transported,  would 
seem  to  be  either  Sweden  or  Norway — the  German 
Ocean  intervening  between  these  countries  and  Ice- 
land. It  is  supposed  that  these  blocks  have  been  trans- 
ported in  icebergs  at  a  period  when  the  ocean  swept 
over  the  countries  where  they  were  originally  formed, 
and  where  they  now  are  found. 


281 


FOSSIL  REMAINS. 

No  department  of  geology  is  more  attractive  than  this. 
It  seems  to  open  a  new  volume  of  the  world's  history, 
and  to  unfold  the  archives  which  have  been  sealed  in 
oblivion  for  ages.  It  is  impossible,  in  the  present 
sketch,  to  present  more  than  a  brief  outline  of  this  in- 
teresting topic.  It  must  be  sufficient  to  say,  that  the 
vestiges  of  trees,  plants,  and  shrubs ;  of  insects,  birds, 
fishes,  and  quadrupeds;  are  found  imbedded  in  the 
strata  of  the  earth :  and,  what  is  most  wonderful,  these 
are,  for  the  most  part,  of  species  now  extinct  It  must 
be  added,  that  the  remains  of  animals  and  vegetables 
are  found  in  climates  repugnant  to  their  nature ;  as, 
for  instance,  those  of  plants  and  animals  fitted  only  to 
the  tropics  are  found  abundantly  even  along  the  mar- 
gin of  the  Arctic  Sea. 

Among  the  fossil  animals  are  the  dinotherium*,  an 
herbivorous  quadruped,  18  feet  in  length,  and  holding 
an  intermediate  place  between  the  tapir  and  the  mas- 
todon ;  the  megatherium,  of  the  sloth  species,  covered 
with  a  bony  coat  of  armor,  like  the  armadillo,  and 
exceeding  the  rhinoceros  in  bulk ;  the  ichthyosaurus, 
or  fish  lizard,  resembling  the  porpoise,  and  sometimes 
30  feet  in  length ;  the  plesiosaurus,  having  the  head 
of  a  lizard,  the  teeth  of  a  crocodile,  the  tail  of  a  quad- 
ruped, ribs  like  those  of  the  c  name  lion,  paddles  like  a 
whale,  and  the  neck  of  a  serpent ;  the  pterodactyl^ 
with  a  neck  like  a  bird,  wings  like  a  bat,  and  a  body 
like  a  lizard  ;  and  the  iguanadou,  an  enormous  lizard, 
sometimes  70  feet  in  length. 

These  are  the  remains  of  some  of  the  wonderful 
24* 


animals  found  in  the  more  ancient  strata.  Among  the 
more  recent  formations,  are  the  remains  of  the  mam- 
moth and  mastodon ;  birds  resembling  the  woodcock, 
quail,  cormorant,  owl,  and  buzzard ;  fishes  of  a  thou- 
sand forms;  and  shells  in  countless  abundance,  and 
of  infinitely  diversified  forms. 

CHANGES  OF  THE  EARTH'S  SURFACE. 

No  principle,  in  geology,  is  better  ascertained  by 
facts,  than  that  many  successive  destructions  and  reno- 
vations have  taken  place  on  the  surface  of  our  globe. 
We  are  apt  to  imagine  that  all  the  great  revolutions  of 
the  earth  have  been  sudden  and  violent,  and  some  of 
these  have  doubtless  been  so  ;  an  instance  of  this  kind 
is  that  recorded  by  Moses,  and  which,  in  consideration 
of  the  great  revolution  which  was  effected,  and  the 
new  aspect  which  the  world  presented,  is  properly 
spoken  of  as  a  creation.  But,  in  general,  we  have 
reason  to  believe  that  the  mutations  and  revolutions 
which  have  been  wrought  upon  the  globe,  for  a  series 
of  ages,  have  been  the  work  of  great  and  powerful 
agents  still  in  operation,  and  still  accomplishing  their 
destined  task  of  change  and  revolution. 

There  are  two  great  antagonist  powers  in  nature  — 
the  aqueous  and  igneous.  These  are  visible,  and  in 
operation,  at-  the  present  hour.  The  former,  as  in 
springs,  rivers,  tides,  frosts,  and  rain,  is  constantly 
employed  in  the  disintegration  of  rocks,  and  in  the 
degradation,  or  levelling,  of  land.  The  latter,  by  vol- 
canoes and  earthquakes,  is,  on  the  other  hand,  employed 
in  restoring  the  elevation  and  inequalities  of  the  sur- 
face. Were  there  no  such  compensating  power  of 


GEOLOGY.  283 

elevation,  a  time  would  come  when  the  whole  materials 
of  the  loftiest  mountains  would  be  transported  to  the 
ocean,  and  when  the  whole  earth  would  be  reduced  to 
a  saline  marsh. 

Among  the  aqueous  instruments  of  change,  we  may 
notice  rain,  which  is  constantly  at  work  in  dissolv- 
ing the  hardest  substances,  and  carrying  them  down 
from  elevated  to  lower  situations.  This  operates  on 
a  mighty  scale,  and  is  sufficient  to  account  for  the 
formation  of  some  of  the  great  valleys  of  the  earth. 
The  ocean,  by  constant  attacks  upon  its  coasts,  grad- 
ually fritters  away  the  rocks,  and  has  been  known  to 
destroy  large  tracts  of  country  by  forcing  its  waters 
into  the  interior  of  continents  ;  numerous  instances  of 
such  irruptions  are  on  record.  But  while  the  sea  is 
thus  a  powerful  agent  of  destruction,  it  is,  like  the 
rivers,  instrumental  in  the  reproduction  of  land.  The 
rocks  and  sand  washed  away  from  one  place  are  car- 
ried, by  tides  and  currents,  far  into  the  ocean,  where 
they  are  deposited  in  strata,  and  in  course  of  time  form 
shoals  and  banks,  which  afterwards  become  promon- 
tories and  islands.  Marine  currents  are  numerous,  and 
tortuous  in  their  course  ;  and,  like  rivers,  carry  in  sus- 
pension abundance  of  mineral  matter,  which  they 
deposit  at  different  places.  Hence,  in  inland  seas, 
and  even  on  the  borders  of  the  ocean,  it  is  sometimes 
scarcely  possible  to  prevent  a  harbor  from  filling  up. 

Among  the  igneous  causes  of  change  in  the  earth's 
surface,  are  volcanoes  and  earthquakes^  which  are  in- 
separably connected,  and  result  from  the  same  causes. 
The  former  are  chiefly  confined  to  certain  geographical 
limits ;  some  are  periodical,  while  others  are  in  a  state 


284  GEOLOGY. 

of  constant  activity.  Stromboli,  in  one  of  the  Lipari 
Isles,  has  never  ceased  its  action  during  a  period  of 
more  than  2000  years  ;  while  Vesuvius  and  Etna  give 
forth  eruptions  only  at  intervals,  and  others  have  been 
dormant  for  ages. 

In  the  snowy  regions  of  the  Andes,  the  effects  of  an 
eruption  are  terrific  ;  for  not  only  are  torrents  of  lava 
ejected,  but  the  intense  heat  melts  the  snow,  which 
causes  inundations,  carrying  the  volcanic  sand,  stones, 
and  rocks,  down  with  desolating  fury  upon  the  plains 
below.  Iceland  is  entirely  of  volcanic  origin  ;  and  so 
intense  has  been  the  volcanic  action,  that  Hecla  has 
sometimes  continued  in  a  constant  state  of  eruption  for 
six  years,  shaking  the  whole  island,  and  causing  great 
changes  in  its  surface.  In  1783,  another  volcanic 
mountain  in  Iceland,  called  Skaptartoyul,  burst  forth, 
and,  throwing  out  a  torrent  of  lava  into  an  adjacent 
river,  completely  dried  it  up.  Not  only  did  the  lava  fill 
the  channel,  which  was  600  feet  deep  and  200  wide, 
but  it  overflowed  the  neighboring  fields ;  filled  up  an 
extensive  lake  ;  and,  advancing  against  an  ancient  mass 
of  lava,  melted  it  down — blowing  up  large  fragments 
of  rocks,  in  its  progress,  to  the  height  of  150  feet :  not 
yet  arrested,  it  continued  its  terrific  course,  filled  the 
deep  abyss  which  the  great  waterfall  of  Steppafoss 
had  been  hollowing  out  for  ages,  and  then  spread  in 
various  directions,  carrying  ruin  and  destruction  over 
the  country.  Of  the  two  streams  of  lava  which  flowed 
from  the  mountain  in  opposite  directions,  one  was  40, 
and  the  other  50,  miles  in  length ;  the  breadth  varied 
from  7  to  15  miles,  while  the  ordinary  height  of  both 


GEOLOGT.  285 

currents  was  100  feet,  though,  in  narrow  defiles,  it 
sometimes  amounted  to  600. 

This  awful  eruption  continued  two  years ;  and  a  trav- 
eller, who  visited  the  tract  eleven  years  afterwards, 
found  columns  of  smoke  still  rising  from  parts  of  the 
lava,  and  several  rents  filled  with  hot  water.  No  fewer 
than  twenty  villages  were  destroyed  on  this  occasion ; 
and  more  than  9000  of  the  inhabitants  perished. 

The  amazing  effects  of  volcanoes  almost  surpass 
conception;  mountains  of  great  height  have  been 
thrown  up  in  a  single  day,  and  have  taken  their  rank 
among  the  permanent  elevations  of  the  globe.  In 
1759,  Jorullo,  hi  Mexico,  was  elevated,  in  the  space  of 
two  months,  into  several  cones  —  the  central  one  being 
1600  feet  above  the  level  of  the  plain.  Forty  years 
afterwards,  when  Humboldt  visited  the  place,  he 
found  the  mighty  masses  of  lava  still  so  hot,  that  he 
was  able  to  light  his  cigar  at  the  depth  of  a  few  inches. 
Two  small  streams,  which  had  disappeared  during  the 
eruption,  afterwards  burst  forth  as  hot  springs  hi  a 
position  remote  from  their  former  course.  Such  is  the 
expulsive  power  of  volcanoes,  that  Cotopaxi  has  been 
known  to  project  rocks,  more  than  100  tons  in  weight, 
to  the  distance  of  nine  miles. 

Nor  are  volcanoes  confined  to  the  land  ;  they  some- 
times burst  forth  from  the  middle  of  the  sea,  displacing 
the  waters,  and  rearing  up  islands  to  the  height  of 
100  feeL 

Earthquakes  are  remarkable  for  the  extent  of  coun- 
try over  which  they  operate.  The  shock  of  an  earth- 
quake in  Chili,  in  1822,  was  simultaneously  felt 
throughout  a  space  of  1200  miles,  from  north  to  south. 


286  GEOLOGY. 

During  the  convulsions  of  an  earthquake,  the  surface 
of  the  earth  undulates  like  a  boiling  liquid  ;  the  sea 
heaves  and  swells  as  in  a  tempest ;  edifices  are  thrown 
into  heaps  of  ruins,  and  enormous  fragments  of  rocks 
are  detached  from  the  mountains.  In  some  instances, 
whole  cities  have  been  ingulfed  in  the  space  of  a  few 
minutes ;  and  extensive  districts  of  country,  teeming 
with  wealth  and  prosperity,  have  been  suddenly  con- 
verted into  ghastly  spectacles  of  desolation. 

The  explanation  of  these  sublime,  yet  terrific  phe- 
nomena, is  to  be  found  in  the  action  of  heat,  generated 
by  chemical  causes  in  the  bowels  of  the  earth.  When 
this  has  melted  vast  masses  of  rock  into  a  flood  of  lava. 
the  boiling  flood  seeks  vent,  and,  in  its  egress,  rends 
every  thing  asunder  which  obstructs  its  path.  There 
is  reason  to  believe  that  every  portion  of  the  earth  has 
been  at  successive  periods  covered  by  water,  and  that 
the  present  elevations,  even  including  the  Andes  and 
the  Alps,  have  been  upheaved  from  the  bottom  of  the 


MISCELLANEOUS  TOPICS. 

The  difference  between  the  former  and  the  present 
temperature  of  northern  latitudes,  is  a  highly  interest- 
ing topic  in  geology.  It  is  a  fact  fully  admitted  that 
the  climate  of  the  northern  hemisphere  was  once  much 
hotter  than  it  is  at  present.  Fossil  plants,  and  animals 
analogous  to  species  which  only  subsist,  at  present,  in 
tropical  countries,  are  found  strewed  over  the  northern 
parts  of  Europe.  To  account  for  the  change  of  cli- 
mate thus  indicated,  various  theories  have  been  sug- 
gested ;  but  the  most  probable  one  is,  that  the  ocean 


GEOLOGY.  287 

and  land  had  once  a  different  arrangement  from  the 
existing  one,  and  that,  at  a  former* period,  currents 
flowing  from  the  tropical  regions,  and  other  circum- 
stances tending  to  the  same  point,  contributed  to  soften 
the  temperature  of  those  regions  which  have  since 
become  frigid.  Various  attempts  have  been  made  to 
account  for  the  deluge  upon  geological  principles.  It 
has  been  suggested  that  an  elevation  of  the  bottom  of 
the  sea,  with  a  corresponding  depression  of  the  moun- 
tains, making  nearly  a  level  surface  over  the  earth, 
enabled  the  accumulated  waters  to  spread  over  the 
whole  extent  of  the  globe.  But  this  supposition  ap- 
pears inconsistent  with  the  language  of  Scripture. 
This  implies  a  vast  increase  of  the  waters  upon  the 
earth :  as  we  cannot  assign  any  natural  cause  for  this, 
we  must  refer  it  to  the  miraculous  agency  of  that 
mighty  Being  whose  stupendous  operations  sink  into 
comparative  insignificance  the  entire  creation  of  a 
globe  like  ours. 

The  age  of  the  earth,  deduced  from  the  archives 
of  nature,  as  recorded  in  the  rocks  of  the  earth's  sur- 
face, has  been  supposed  to  be  millions  of  years.  This 
has  been  thought  to  impugn  the  veracity  of  the  Mosaic 
history,  which  seems  to  represent  our  globe  as  having 
been  created  about  6000  or  7000  years  ago.  A  proper 
reading  of  the  Bible,  however,  shows  no  incompatibility 
with  the  facts  attested  by  geology.  The  six  days 
spoken  of  in  Genesis,  during  which  the  work  of  crea- 
tion was  performed,  may  have  been  six  indefinite 
periods  of  time,  each  millions  of  years  in  length ;  or, 
what  is  more  probable,  the  six  days  were  of  the  ordi- 
nary length ;  but,  previously  to  the  first  day,  a  vast 


288  GEOLOGY. 

period  of  time  liad  elapsed,  during  which  all  those 
strata  were  formed,  and  those  plants  and  animals  lived, 
the  existence  of  which,  previously  to  our  own  epoch, 
is  so  clearly  proved.  In  this  view,  the  Mosaic  creation 
is  to  be  regarded  as  a  renovation  of  animal  and  vege- 
table life,  and  a  preparation  for  the  reception  of  man. 
That  such  a  work  was  actually  performed  upon  this 
globe,  at  the  period  indicated  by  the  Scriptures,  is  as 
clearly  demonstrated  by  geology  as  by  holy  writ ; 
for,  while  we  find  the  vestiges  of  other  races  of  plants 
and  animals,  that  lived  ages  ago,  we  find  no  traces  of 
man  himself  which  indicate  his  existence  at  a  period 
earlier  than  that  which  the  Bible  establishes. 


MINERALOGY. 


THE  object  of  this  science  is,  to  describe  the  general 
composition,  characters,  varieties,  forms,  and  combina- 
tions, of  mineral  bodies.  A  mineral  may  be  described 
as  a  substance  destitute  of  organization  and  vitality, 
found  on  the  surface  of  the  earth,  or  imbedded  at  various 
depths  beneath  it,  in  veins,  or  strata,  which  are  worked 
for  the  extraction  of  such  substances,  by  excavations 
called  mines. 

Mineralogy  may  be  distinguished  from  chemistry,  as 

relating  to  the  forms  and  properties  of  certain  bodies  as 

they  are  presented  to  us  by  nature ;  while  the  latter 

science  instructs  us  how  to  procure  a  multitude  of 

s  xm. — 25 


290  MINERALOGY. 

artificial  products  derived  alike  from  the  animal,  ve- 
getable, and  mineral  kingdom,  and  to  expose  their 
properties,  especially  as  respects  their  rule  of  com- 
bination. 

Mineralogy  is  likewise  to  be  distinguished  from 
geology,  with  which,  however,  it  is  intimately  con- 
nected. It  is  the  province  of  the  geologist  to  investigate 
the  general  structure  of  the  earth,  and  the  nature  and 
arrangement  of  the  great  masses  of  which  it  is  com- 
posed. The  mineralogist,  on  the  other  hand,  confines 
his  attention  to  individual  portions  of  unorganized  mat- 
ter, distinguished  by  peculiar  and  specific  characters. 

In  the  study  of  geology,  it  is  of  the  utmost  impor- 
tance to  be  enabled  to  examine  the  objects  of  research, 
as  they  are  formed  by  nature,  and  to  ascertain  their 
relative  connection  and  arrangement  in  the  formation 
of  rocks,  mountains,  plains,  subterraneous  strata,  and,  in 
general,  of  all  the  great  masses  the  assemblage  of 
which  constitutes  the  solid  shell,  or  exterior  surface,  of 
the  terrestrial  globe.  The  nature  and  properties  of 
minerals  may  be  investigated  and  ascertained,  without 
any  reference  to  the  situations  in  which  they  are  pro- 
duced. 

Thus  connected  as  mineralogy  is  with  chemistry  on 
the  one  hand,  and  with  geology  on  the  other,  it  dis- 
plays features  sufficiently  distinct  from  those  of  either  ; 
yet,  at  the  same  time,  the  objects  of  these  sciences  so 
far  correspond  that  a  complete  knowledge  of  mineral- 
ogy cannot  be  obtained  without  a  previous  acquaint- 
ance with  chemistry  ;  nor  can  the  information  which 
these  sciences  form,  when  united,  relative  to  the  unor- 
ganized productions  of  nature,  be  applied  to  a  more 


MINERALOGY.  291 

exalted  purpose  than  that  of  aiding  our  researches 
concerning  geology. 

Mineral  substances  may  be  discriminated  from  each 
other  by  their  mode  of  crystallization  or  aggregation ; 
and  the  optical  properties  depending  upoa  their  pecu- 
liar forms,  by  their  physical  characters,  as  color,  lustre, 
transparency,  hardness,  consistency,  density,  or  specific 
greasily  ;  as  also,  in  some  cases,  by  their  taste  or  odor, 
by  their  relations  to  electro-magnetism,  and  finally  by 
their  chemical  constitution.  The  manner  in  which  the 
particles  of  minerals  are  arranged,  or  their  crystalliza- 
tion, is  a  curious  and  interesting  subject  of  inquiry. 
Any  or  all  of  these  various  qualities  and  affections  may 
be  taken  into  consideration  in  forming  classical  arrange- 
ments of  bodies  belonging  to  the  mineral  kingdom  of 
nature.  Hence  a  diversity  of  systems  and  arrange- 
ments have  been  contrived  by  various  mineralogical 
writers.  In  general,  we  regard  the  mineral  kingdom 
as  divided  into  four  departments — earths,  metals,  salts, 
and  combustibles. 

Within  the  narrow  limits  of  this  sketch,  we  have 
room  only  to  mention  a  few  of  the  most  important 
mineral  bodies.  One  of  these  is  lime :  this  is  never 
found  pure,  but  is  obtained  artificially  by  burning 
limestone  till  the  carbonic  acid  which  it  contains  is 
driven  off.  Limestone  is  of  various  kinds,  the  hardest 
of  which  is  marble.  Lime  enters  into  the  composition 
of  a  number  of  earthy  or  stony  minerals,  and  exists  in 
such  abundance,  that  some  geologists  have  estimated  that 
it  exists,  in  the  crust  of  the  globe,  in  the  proportion  of 
one  eighth  of  the  whole.  This  substance,  and  its  com- 
pounds, are  of  infinite  importance  and  utility  to  man. 


292  MINERALOGY. 

Chalk  is  a  carbonate  of  lime,  but  is  far  less  abundant 
than  compact  limestone  ;  it  contains  flints  and  animal 
remains. 

Coal  has  been  generally  ranked  among  minerals 
because  its  basis  is  pure  carbon  ;  but  it  is  generally  sup- 
posed to  be  of  vegetable  origin,  as  the  substance  which 
lies  upon  the  coal  is  always  filled  with  vegetable  re- 
mains, and  a  wood-like  appearance  may  be  traced 
through  every  species  of  coal,  even  the  most  compact. 
The  harder  species,  which  burns  without  smoke,  is  called 
anthracite.  There  are  few  countries  in  which  coal  is 
not  found  more  or  less  abundantly.  England  is  re- 
markable for  its  coal  mines.  In  the  United  States,  it  is 
most  abundant  in  Pennsylvania. 

Mineral  salt  is  found  in  beds  or  masses.  It  is  not  a 
simple  substance,  but  is  composed  of  earth,  soda,  and 
muriatic  acid.  It  is  one  of  the  most  plentiful  sub- 
stances in  nature,  being  not  only  dug  out  of  the  earth, 
but  forming  a  thirteenth  part  of  the  waters  of  the 
ocean.  Salt  or  brine  springs  are  found  in  many  coun- 
tries, affording  immense  quantities  of  salt  by  artificial 
evaporation.  Rock-salt  is  sometimes  found  on  the 
tops  of  mountains,  far  above  the  region  of  perpetual 
snow.  In  Hungary  and  Poland,  there  is  an  immense 
body  of  rock-salt  at  the  foot  of  the  Carpathian  Moun- 
tains. The  salt  mine  of  Wieliczka,  near  Cracow,  in 
Poland,  has  been  worked  since  the  year  1251 :  the  salt 
commences  about  200  feet  below  the  soil,  and  the  mine 
has  been  wrought  to  the  depth  of  900  feet.  The  gal- 
leries are  completely  dry,  and  the  mine  contains 
springs  of  both  fresh  and  salt  water.  In  this  mine  are 
several  chapels  for  the  workmen,  some  of  which  are 


MINERALOGY.  293 

furnished  with  altars,  crucifixes,  and  statues,  all  of  solid 
salt.  In  Moldavia  is  a  mountain  of  salt,  which  in  many 
parts  is  not  covered  even  with  soil.  The  annual  pro- 
duction of  salt,  in  England,  has  been  estimated  at 
500,000  tons. 

Sulphur  is  a  primitive  substance,  and  takes  its  rank 
among  the  combustibles.  It  is  found  not  only  in  the 
mineral  kingdom,  but  in  the  vegetable  and  animal ; 
though,  in  the  two  latter,  it  occurs  so  rarely,  that  all  the 
vast  commercial  demands  for  it  are  supplied  from  the 
former  source.  It  is  found  nearly  pure,  and  is  then 
termed  notice  sulphur.  It  is  also  found  in  combination 
with  several  of  the  metals  ;  and,  in  the  state  of  an  acid, 
it  occurs  combined  with  some  of  the  earths  and  metals. 
It  is  sometimes,  though  rarely,  found  in  veins  in  primi- 
tive mountains :  its  common  repository  is  in  beds  of 
gypsum,  where  it  appears  in  rounded  masses.  Volca- 
noes abound  with  sulphur,  which  is  thrown  up  in  the 
rifts  and  cavities  of  the  lava  in  the  neighborhood  of 
their  craters.  Volcanic  sulphur  is  found  in  Italy,  Ice- 
land, and  America,  in  volcanoes  yet  in  activity.  The 
volcanoes  of  the  Cordilleras,  in  Quito,  yie';d  it  in  great 
abundance,  and  very  pure.  But  the  most  remarkable 
deposit  of  volcanic  sulphur  is  that  of  Solfatara,  near 
Naples,  in  a  kind  of  sunken  plain,  surrounded  oy  rocks, 
which  is  regarded  as  the  crater  of  an  ancient  volcano ; 
and  from  this  place,  ever  since  the  age  of  Pliny,  has 
been  obtained  a  considerable  portion  of  the  sulphur 
consumed  in  Europe.  The  uses  of  this  substance  in 
chemistry,  medicine,  and  the  arts,  are  important,  and 
sufficiently  well  known. 

The  diamond  may  be  classed  in  the  same  rank  with 
25* 


294  MINERALOGY. 

sulphur,  being  a  combustible,  and  not,  as  was  formerly 
believed,  an  earthy  or  stony  substance.  When  ex- 
posed to  a  current  of  air,  and  heated  to  the  temperature 
of  melted  copper,  it  is  found  to  be  gradually,  but  com- 
pletely, inflammable.  By  this  process  it  may  be  wholly 
converted  into  carbonic  acid,  and  therefore  consists  of 
pure  carbon.  Diamonds  are  either  colorless,  or  yel- 
low, blue,  green,  brown,  or  rose-red.  They  are  always 
found  in  detached  crystals,  and,  in  their  primitive  form, 
are  eight-sided.  Although  the  diamond  is  the  hardest 
substance  in  nature,  it  may  be  readily  cleaved  in  par- 
ticular directions.  It  may  also  be  worn  out  by  long 
use  and  continual  friction.  In  the  shops  of  wholesale 
glaziers,  where  it  is  in  constant  requisition  for  the  pur- 
pose of  cutting  glass,  it  is  often  rendered  useless  in  the 
space  of  two  months.  It  may  be  presumed,  however, 
that  it  travels  over  many  miles  of  glass,  before  it  is 
worn  too  smooth  for  use. 

Diamonds  can  be  cut  and  polished  only  by  friction 
against  each  other,  or  rather  by  means  of  their  own 
powder.  They  are  sometimes  sawed  by  a  delicate 
iron  wire,  coated  by  their  own  powder.  This  art  was 
unknown  till  the  year  1486,  and  of  course  the  ancients 
could  not  have  been  acquainted  with  the  great  brilliancy 
of  the  diamond,  as  this,  in  a  great  degree,  depends  on 
the  art  of  the  lapidary.  Its  uses  are  well  known ;  its 
value  increases  in  a  much  greater  ratio  than  its  weight. 
The  largest  known  is  about  the  size  of  a  pigeon's  egg, 
and  was  formerly  possessed  by  the  empress  of  Russia. 
It  is  said  to  have  been  sold  for  416,666  dollars,  and 
a  pension  of  16,666  dollars  for  life.  India  and  Brazil 
are  almost  the  only  countries  known  to  afford  this  pre- 
cious stone. 


MINERALOGY.  29o 

METALS  next  claim  our  attention.  These  are  simple 
substances,  not  one  of  them  yet  having  been  decom- 
posed. In  weight,  the  metals  far  exceed  the  earths ; 
the  heaviest  of  the  latter  is  only  five  times  heavier 
than  water,  while  the  lightest  of  the  metals  is  six  times 
heavier.  Beaten  gold  is  nineteen  times  heavier,  and 
beaten  platina,  the  heaviest  of  all,  is  twenty-three  times 
heavier  than  water.  Each  metal  possesses  a  color 
peculiar  to  itself.  Some  of  them  are  exceedingly 
ductile,  as  is  manifested  by  the  extremely  fine  wires 
into  which  they  are  drawn.  Most  of  them  are  good 
conductors  of  electricity  and  heat,  and  the  greater 
number  are  elastic  and  flexible. 

The  only  metals  known  to  the  ancients  were  gold, 
silver,  copper,  iron,  tin,  lead,  and  mercury ;  but  dis- 
coveries have,  from  time  to  time,  added  to  the  catalogue 
until  it  has  been  swelled  to  the  number  of  twenty -eight, 
independently  of  those  which  have  very  lately  been 
discovered  as  the  bases  of  some  of  the  earths  and  two 
of  the  alkalies.  Of  these  twenty-eight  metals,  eleven 
only  have  the  important  property  of  malleability  ;  the 
remainder  therefore  have  been  termed  brittle  metals. 
The  malleable  metals  are  platina,  gold,  silver,  mercury, 
lead,  copper,  tin,  iron,  zinc,  palladium,  and  nickel 
The  brittle  metals  are  arsenic,  antimony,  bismuth, 
cobalt,  manganese,  tellurium,  titanium,  tantalium, 
molybdena,  tungsten,  chrome,  osmium,  indium,  rho- 
dium, uranium,  and  cerium. 

Gold  was  probably  the  first  metal  that  attracted  the 
notice  of  mankind,  and  was  applied  to  purposes  of 
utility  or  ornament.  As  it  is  not  rusted  or  decomposed 
by  air  or  moisture,  it  preserves  its  metallic  lustre,  and 


296  MINERALOGY. 

is  generally  found,  in  its  metallic  state,  nearly  pure. 
The  ductility  of  gold,  and  its  easy  fusibility,  were  prop- 
erties that  enabled  the  first  rude  artificers  to  mould  it 
with  facility  into  various  forms,  and  contributed,  no  doubt, 
to  stamp  a  high  vi!ue  on  this  metal  in  early  ages  —  a 
value  which  it  has  retained,  from  its  imperishable  nature 
and  comparative  rarity.  It  is  probable  that  gold,  sil- 
ver, and  afterwards  copper,  were  for  a  long  time  the 
only  metals  used  by  mankind,  as  they  are  the  only 
ones  that  occur  in  any  considerable  quantities  in  a 
native  state,  or  near  the  surface  of  the  earth.  Hence, 
perhaps,  originated  the  tradition  of  the  golden,  the  sil- 
ver, and  the  brazen  ages.  Though  gold  is  less  abun- 
dant than  many  other  metals,  it  is  distributed  over 
almost  every  part  of  the  known  world,  either  in  veins, 
or  disseminated  through  the  sands  of  rivers  or  alluvial 
soil,  in  loose  grains  and  detached  masses.  The  gold 
collected  by  washing  the  sand  of  rivers  is  called 
gold  dust.  In  malleability,  it  is  superior  to  all  other 
metals ;  a  single  grain  of  gold  will  cover  the  space 
of  '56  square  inches,  when  beaten  out  to ,  its  full  ex- 
tent ;  yet  the  tenacity  of  this  metal  is  so  great,  that  a 
wire  one  tenth  of  an  inch  in  diameter  will  hold  a 
weight  of  500  pounds  without  breaking.  When  used 
for  mechanical  purposes,  or  for  coin,  it  is  alloyed  with 
silver  or  copper,  to  increase  its  hardness. 

Platina,  the  heaviest  of  all  known  substances,  is  of  a 
grayish-white  color,  approaching  that  of  silver,  but 
with  less  lustre.  It  is  somewhat  inferior,  in  hardness 
to  iron.  The  hottest  furnace  cannot  melt  it,  though  i* 
may  be  fused  in  the  focus  of  a  powerful  mirror,  or  by 
a  blowpipe  with  oxygen  gas.  It  does  not  oxidate  in 


MINERALOGY.  297 

the  air,  or  a  strong  heat ;  and  its  hardness,  infusibility, 
and  resistance  to  those  elements,  indicate  the  important 
uses  to  which  it  may  be  applied.  Thus  it  is  employed 
for  crucibles,  spoons,  evaporating  vessels,  pendulums, 
pyrometers,  &c.  It  is  found  in  grains,  in  alluvial  soil, 
in  South  America  ;  the  grains  are  commonly  no  larger 
than  a  pea,  although  masses  have  occurred  of  the  size 
of  a  pigeon's  egg. 

Silver,  when  pure,  is  very  nearly  white.  In  lustre 
it  is  superior  to  gold,  but  in  malleability  somewhat  in- 
ferior. It  is  not  oxidated  by  exposure  to  the  air,  but 
only  acquires  a  tarnish.  The  ores  of  silver  are  more 
numerous  than  those  of  gold,  and  they  occur  prin- 
cipally in  veins,  in  mountainous  districts ;  sometimes 
at  great  elevations.  The  mine  of  Jauricocha,  in  Peru, 
is  about  3  miles  above  the  sea,  and  contains  a  pro- 
digious mass  of  porous,  brown  iron-stone,  half  a  mile 
square  and  100  feet  deep,  thoroughly  interspersed 
with  pure  silver.  The  mines  in  this  quarter  have 
yielded  40,000,000  dollars  in  a  year.  Native  silver  is 
found,  in  considerable  masses,  in  some  mining  districts 
that  contain  silver  ores ;  in  others  it  occurs  rarely,  and 
in  small  quantities.  Koningsberg,  in  Norway,  has  fur- 
nished the  largest  solid  masses  of  native  silver,  some  of 
which  have  exceeded  200  pounds  in  weight.  When  it 
is  coined,  it  is  alloyed  with  copper. 

Mercury,  or  quicksilver,  differs  remarkably  from  all 
other  metals,  by  its  fluidity.  It  is  thirteen  times  heavier 
than  water ;  and  iron  will  float  in  it  It  becomes  solid  at 
40  degrees  below  zero  of  Fahrenheit ;  and  in  this  state 
it  is  malleable  and  flexible.  Mercury  is  found  native, 
but  most  generally  in  combination  with  other  minerals. 


298  MINERALOGY. 

When  combined  with  sulphur,it  is  called  cinnabar,  which 
is  the  red  pigment  otherwise  known  as  vermilion.  The 
ores  of  mercury  are  not  widely  distributed  over  the 
globe:  almost  the  only  mines  known  are  those  of 
Idria  in  Germany,  Almoden  in  Spain,  and  Guanca  Vel- 
ica  in  Peru.  The  uses  of  this  metal,  in  medicine,  the 
arts,  and  experimental  philosophy,  are  numerous  ;  but 
its  chief  use  is  in  the  separation  of  gold  and  silver 
from  their  ores,  by  a  process  called  amalgamation. 
When  mercury  is  amalgamated  with  tin,  and  laid  on 
glass,  it  forms  mirrors. 

Copper,  before  the  general  introduction  of  iron, 
appears  to  have  been  used  for  almost  every  purpose  to 
which  the  latter  metal  has  since  been  applied.  It  was 
made  into  swords  and  other  edge  tools ;  a  considerable 
degree  of  hardness  being  communicated  to  it  by  an 
alloy  of  tin.  Native  copper  is  of  a  yellow-red  color, 
and  is  often  found  nearly  pure,  in  large  masses,  on  the 
surface  of  the  earth.  This  was  probably  the  cause  of 
its  being  brought  into  early  use  ;  it  is  obtained  from  most 
of  its  ores  with  considerable  difficulty.  These  ores  are 
numerous.  The  uses  of  copper  in  all  its  various  states 
are  almost  endless,  and  only  inferior  to  those  of  iron. 
Alloyed  with  certain  proportions  of  zinc,  it  forms  brass, 
pinchbeck,  tinsel,  and  Dutch  gold,  in  imitation  of  gold- 
leaf.  With  a  small  proportion  of, tin,  it  forms  bell- 
metal,  and  bronze  for  statues  and  cannon ;  with  a 
larger  proportion,  it  forms  speculum-metal  for  reflect- 
ing-telescopes. 

Tin  is  the  lightest  of  the  ductile  metals.  It  is  of  a 
white  color,  nearly  approaching  to  that  of  silver.  It  is 
easily  fusible,  and  produces  a  peculiar  cracking  noise 


MINERALOGY.  299 

when  bent.  It  has  not  hitherto  been  found  in  a  native 
state,  and  its  ores  are  not  widely  distributed  over  the 
globe.  The  uses  of  tin  are  numerous  and  important. 
Some  of  them  have  been  already  specified.  With 
lead  it  forms  pewter,  and  solder.  It  is  employed  in 
the  preparation  of  tin-plate,  which  consists  of  sheet- 
iron  tinned  over,  to  prevent  rusting.  It  is  also  applied 
to  the  inner  surface  of  copper  vessels  designed  for 
cooking,  to  prevent  the  injurious  effects  arising  from 
the  copper.  The  chief  mines  of  this  metal  are  those 
of  Cornwall,  in  England,  and  Banca,  in  the  East 
Indies. 

Lead  is  of  a  bluish-gray  color,  and  is  very  malle- 
able, ductile,  inelastic,  and  soft.  It  has  hardly  ever 
been  found  native,  but  its  ores  are  numerous.  The 
almost  constant  occurrence  of  silver  with  lead,  seems 
to  indicate  that  these  metals  have  a  common  origin. 
By  friction,  this  metal  exhales  a  peculiar  and  somewhat 
disagreeable  odor.  It  would  scarcely  be  possible  to 
enumerate  all  the  valuable  purposes  to  which  lead  is 
applied  in  the  arts,  in  medicine,  and  in  the  common 
wants  of  man.  Among  its  less  obvious  uses,  lead  is 
employed  to  glaze  pottery,  and  its  oxide  enters  into  the 
composition  of  glass.  Four  parts  of  lead  and  one  of 
antimony,  with  a  little  copper,  form  type-metal. 

Iron  is  an  ingredient  in  almost  every  rock,  from  the 
oldest  primitive  to  the  newest  alluvium,  and  also  in  very 
many  earthy  and  metalliferous  minerals,  and  in  all  soils ; 
it  is,  therefore,  considered  to  be  the  most  abundant  and 
most  generally  diffused  of  all  the  metals.  Whenever 
found,  and  with  whatever  combined,  it  is  mostly  in  the 
state  of  an  oxide,  except  when  united  with  sulphur. 


300  MINERALOGY. 

When  pure,  it  is  of  a  bluish-gray  color,  and  of  a  gran- 
ular texture ;  it  is  hard,  ductile,  and  malleable,  and  is 
the  most  tenacious  of  metals,  next  to  gold.  It  has  the 
remarkable  property  of  being  magnetic  ;  and  so  readily 
is  polarity  acquired  by  iron,  that  a  bar  remaining  a 
long  time  in  a  vertical  position  becomes  magnetic ;  the 
north  pole  is  always  at  the  lower  extremity.  Iron  has 
been  met  with  in  a  nearly  pure  metallic  state,  in  con- 
siderable masses,  reputed  to  have  fallen  from  the  skies. 
This  meteoric  iron  always  contains  a  portion  of  nickel, 
which,  it  is  worthy  of  remark,  is  also  found,  by  analysis, 
to  be  a  constituent  part  of  all  those  stones  which,  in 
various  parts  of  the  world,  have  been  known  to  fall 
from  the  atmosphere,  and  are,  therefore,  denominated 
meteoric  stones.  A  mass  of  meteoric  iron  was  found 
in  Peru,  weighing  15  tons.  It  was  compact  in  sub- 
stance externally,  and  marked  with  impressions  as  if 
of  hands  and  feet,  of  enormous  size,  and  of  the  claws 
of  birds ;  internally,  it  presented  many  cavities. 

It  is  unnecessary  to  attempt  the  enumeration  of  the 
uses  to  which  iron  is  put  by  the  ingenuity  of  man. 
Steel  is  an  artificial  combination  with  carbon.  Plum- 
bago, or  black  lead,  is  a  natural  combination  of  the 
same  materials. 

Antimony  occurs,  in  the  native  state,  alloyed  by  iron 
and  silver ;  in  its  ores,  it  is  combined  with  sulphur  and 
other  materials.  Zinc  occurs  in  similar  combinations. 
Nickel  is  a  rare  metal,  and  is  found  in  the  state  of  an 
oxide,  and  also  combined  with  arsenic.  Arsenic  is 
involved,  in  small  portions,  in  several  of  the  native 
metals,  and  in  the  ores  of  some  others.  Cobalt  is  not 
very  plentiful :  in  its  ores,  it  occurs  with  iron  and  arsenic 


MIMEEALOGY.  801 

The  remainder  of  the  metals  are  comparatively  rare, 
and  do  not  require  a  minute  description. 

The  whole  of  the  elementary  constituent  parts  of 
minerals,  at  present  known,  are  not  fewer  than  fifty. 
They  comprise  twenty-eight  metals,  the  bases  of  ten 
earths,  and  of  three  alkalies,  with  nine  other  elementary 
substances.  Since  the  discovery  of  the  metallic  nature 
of  the  earths,  the  chemist  can  no  longer  regard  them 
as  elements,  but  as  metallic  oxides,  or  unknown  bases 
combined  with  oxygen.  Yet,  as  the  bases  of  the  earths 
never  occur  in  nature  in  an  uncombined  state,  the 
mineralogist  may  still  speak  of  the  earths  as  simple 
substances. 


BOTANY. 


BOTANY  is  the  science  of  the  vegetable  kingdom, 
and  is  one  of  the  most  attractive,  useful,  and  extensive 
departments  of  human  knowledge.  It  is,  above  every 
other,  the  science  of  beauty.  There  are  few  plants 
which  are  .not  beautiful,  considered  as  separate  indi- 
viduals, and  in  all  the  parts  of  their  individual  organi- 
zation ;  and  there  is  a  beauty  in  the  grouping  of  plants, 
whether  as  grouped  by  nature,  or  by  skilful  art,  to 


which  there  is  nothing  equal  in  that  of  any  of  the  other 
productions  of  nature.  The  landscape  is  the  object 
which  mankind  most  generally  admire  ;  and  the  land- 
scape owes  its  principal  if  not  its  only  charms  to  its 
vegetation.  Rocks  have,  no  doubt,  their  grandeur ;  and 
there  is  a  beauty  in  running  waters,  and  even  in  placid 
lakes ;  but,  let  the  rock  be  naked  of  vegetation  down 
to  and  around  its  base,  and  its  grandeur  is  painful, — it 
seems  a  ruin.  So,  also,  if  the  water  is  denuded  of  its 
meadows,  its  thickets,  its  groves,  its  shady  trees,  and  its 
plants  of  humbler  growth,  it  is  no  longer  beautiful ;  for 
an  expanse  of  water,  or  a  rolling  torrent,  amid  perfect 
sterility,  makes  the  contemplation  of  that  sterility  more 
gloomy,  from  the  feeling  that  this  water,  by  being  un- 
productive, is  so  much  of  the  bounty  of  nature  running 
to  waste.  It  is  needless,  however,  to  expatiate  on  this 
part  of  the  subject ;  for  every  one  feels  it  more  forcibly, 
in  the  contemplation  of  nature  itself,  than  it  could  be 
rendered  by  even  the  most  labored  description. 

As  little  is  it  necessary  to  descant  on  the  usefulness 
of  the  study  of  vegetables ;  for  we  have  only  to  look 
around  us,  and  observe  how  much  of  our  food,  our 
clothing,  our  furniture,  our  habitations,  the  implements 
of  our  work,  and  the  instruments  of  all  our  enjoyment, 
is  derived  from  the  vegetable  kingdom,  in  order  to 
see  that  it  is  this  kingdom  which  is  the  grand  founda- 
tion of  all  our  arts,  and  one  of  the  instruments  by 
which  man  has  been  civilized,  and  enabled  to  turn  all 
the  other  productions  of  nature  to  whatever  use  he 
makes  of  them.  For  instance,  there  can  be  no  civili- 
zation without  fire  ;  indeed,  fire  is  one  of  the  chief 
distinctions  of  man,  in  the  lowest  states  of  society,  from 


304  BOTANY.     v 

the  other  animals,  many  of  which  are  superior  to  him 
in  strength,  in  speed,  in  the  acuteness  of  their  senses, 
and  even  in  some  of  their  artifices  :  there  can  be  no 
fire  without  fuel ;  and  all  fuel  is  vegetable.  It  is  by 
means  of  vegetables  —  of  the  timber  which  forms  the 
ship,  and  the  fibres  of  which  the  cordage  and  sails  are 
made  —  that  man  has  been  enabled  to  extend  his  knowl- 
edge to  eveiy  portion  of  the  globe,  and  partake,  at 
most  points  of  its  surface,  of  the  riches  of  all.  No  one 
can  help  admiring  the  exquisite  beauty  of  many  flowers, 
and  the  delicious  flavor  of  many  fruits,  which  are  habit- 
ually brought  from  a  distance  of  many  thousand  miles 
over  the  sea ;  and  for  all  of  these,  and  for  every 
foreign  commodity,  and  for  every  piece  of  foreign  in- 
formation, that  we  can  enjoy  or  obtain,  we  are  indebted 
to  the  vegetable  ship. 

A  subject  which  is  of  so  vast  and  varied  usefulness, 
and  which,  at  the  same  time,  has  so  much  of  beauty  to 
recommend  it,  cannot  receive  too  much  of  our  attention ; 
and,  the  more  to  induce  us  to  bestow  this  attention,  we 
find,  by  experience,  that  the  productions  of  the  vegetable 
kingdom  are  much  more  obedient  to  skilful  cultivation 
than  those  of  any  other  department  of  nature.  Com- 
pare an  ordinary  field  under  crop  with  a  neglected 
common,  of  precisely  the  same  soil,  and  in  a  situation 
exactly  similar,  —  or  compare  a  moderately  cultivated 
garden  with  a  neglected  heath,  —  and  they  appear  as 
if  they  were  not  parts  of  the  same  country. 

Take  some  of  the  most  common,  but,  at  the  same 
time,  the  most  useful,  of  those  vegetables  which  we  cul- 
tivate as  food,  and  consider  what  human  skill  has  done 
for  them.  Where  is  there  a  native  grain  like  wheat,  a 


BOTANY.  305 

native  fruit  like  the  apple,  a  native  bud  like  the  cauli- 
flower, or  a  native  root  like  the  potato  ?  The  last  is  a 
remarkable  instance  of  what  cultivation  can  do ;  and 
its  history  from  the  wild  plant  happens  to  be  known. 
The  potato  is  a  native  of  the  mountains  of  tropical 
America,  and,  when  found  wild  there,  it  is  barely,  if  at 
all,  eatable.  These  are  but  a  few  instances  out  of 
many,  in  which  plants,  naturally  of  little  value,  have 
been  rendered  very  valuable  by  cultivation,  in  climates 
much  less  favored  by  nature  than  those  in  which  they 
are  found  native  ;  but  even  these  may  suffice  to  show 
the  vast  advantage  which  has  been  derived  from  study- 
ing the  nature  of  vegetables ;  and  as  the  number,  of 
which  the  improvement  by  culture  has  been  ascer- 
tained, is  very  small  compared  with  those  of  which  it 
has  not,  the  field  open  for  further  improvement  is  as 
wide  as  it  is  inviting. 

The  history  of  vegetable  science  is  brief  and  imper- 
fect. The  Greek  philosophers,  having  derived  their 
knowledge  principally  from  Asia  and  Egypt,  exam- 
ined the  laws  of  vegetable  life  very  superficially,  from 
their  want  of  means,  and  their  ignorance  of  chemistry. 
They  at  once  arrived  at  general  conclusions,  and 
asserted  that  plants  possessed  rational  souls,  capable 
of  the  mental  powers,  and  indicative  of  the  organiza- 
tion of  animals.  Aristotle,  384  B.  C.,  published  his 
works  on  natural  history,  in  which  he  formed  a  more 
rational  theory,  though  little  corresponding  with  that 
of  the  present  day.  Theophrastus,  the  pupil  of  Aris- 
totle, is  said  to  have  been  the  founder  of  philosophical 
botany  ;  he  wrote  several  works  on  the  subject.  Dios- 
corides  compiled  a  work  containing  a  partial  descrip- 
T  26* 


306  BOTANY. 

tion,  particularly  of  the  medicinal  qualities  of  "200 
plants,  in  the  first  year  of  the  Christian  era ;  and  this 
was  the  only  source  of  botanical  knowledge  for  fifteen 
centuries.  To  this,  Persian  and  Arabian  physicians 
added  200  plants. 

The  elder  Pliny  and  Galen  contributed  also  to  a 
knowledge  of  the  properties  of  plants.  But  the  Ger- 
mans were  first  to  found  historical  botany,  and  to  com- 
mence scientific  classification.  The  Italians  followed, 
and  then  the  Belgians.  The  French  greatly  increased 
the  number  of  plants,  and  reformed  the  nomenclature ; 
so  that,  at  the  beginning  of  the  17th  century,  the  num- 
ber of  species  known  was  5500.  This  number  con- 
tinued to  increase,  by  an  awakened  attention  to  the 
subject,  and  the  united  labors  of  others  in  various 
countries,  until  Linnaeus  appeared  with  his  Species 
Plantarum,  when  the  number  of  plants  known  was  7300. 
Since  this  time,  it  has  increased  most  wonderfully.  A 
more  systematic  or  natural  method  of  arrangement 
has  been  introduced  by  Jussieu,  Condolle,  Mirbel,  and 
others ;  and  the  whole  now  presents,  in  every  depart- 
ment, the  most  attractive  interest.  The  progress  of  the 
science  of  vegetables,  botanical  and  agricultural,  has 
been  unexampled  in  the  history  of  any  other  science. 
But,  however  interesting  this  may  be,  we  lack  time  and 
space  to  notice  it  further.  Chemistry,  the  chief  source 
of  improvement  in  this  branch  of  science,  has  recently 
disclosed,  through  Liebeg  and  others,  the  most  impor- 
tant facts,  as  to  the  nature,  requirements,  and  prop- 
erties, of  fruits  and  plants,  and  shed  a  noonday  light 
on  the  path  of  the  practical  agriculturist. 


307 


VEGETABLE   PHYSIOLOGY,  &c. 


That  portion  of  the  science  of  botany,  which  treats 
of  the  life  and  growth  of  plants,  is  called  vegetable 
physiology,  and  is  one  of  the  most  attractive  portions 
of  the  science.  Of  this  topic,  we  can  only  give  a 
hastjr  outline. 

*  Plants  are  organized  living  bodies,  which,  like  those 
of  animals,  are  composed  of  solids  and  fluids.     They 
are  without  powers  of  locomotion,  and,  it  is  thought, 
of  voluntary  motion.     They  are  fixed  to  the  earth  by 
.oots,  from  which  they  rise  upward  by  a  stem  which 
throws  out  branches  that,  in  their  turn,  give  out  others, 
all  bearing  leaves,  flowers,  fruits,  and  seeds.     The 
word  plant  literally  means  "  fixed  "  or  "  rooted  ;  "  but 
in  botany,  it  signifies  all  productions  of  the  vegetable 
kingdom.     These  are  of  three  kinds  —  herbs,  shrubs, 
and  trees ;  they  are  annual,  perishing  within  the  year ; 
biennial,  flowering  the  second  year,  and  then  perish- 
ing ;  or  perennial,  surviving  many  years.     They  are 
deciduous  when  their  leaves  fade  in  autumn,  and  ever- 
green when  these  are  constantly  renewed,  as  with  all 
resinous  trees.     They  are  indigenous,  or  native,  and 
exotic,  or  foreign.     The  solid  parts  of  plants  consist 
mostly  of  cellular  substance,  woody  fibre,  pith,  bark, 
&c. ;  and  of  fluids  and  juices,  of  various  degrees  of 
consistence,  as  volatile  andjixed  oils,  gums,  resins,  air, 

*  In  the  preparation  of  this  article,  we  are  largely  indebted 
to  a  work  entitled  the  Vegetable  Kingdom,  or  Hand  Book  of 
Plants  and  Fruits,  bj  L.  D.  Chapin,  —  a  work  which  we  hearti- 
ly recommend,  as  combining,  in  a  most  attractive  form,  the 
entertaining  and  useful  facts  of  this  important  subject. 


308  BOTANY. 

water,  &c.  These  are  circulated  in  various  ways, 
and  in  numerous  vessels  and  organs,  each  contain- 
ing particular  substances,  and  performing  peculiar 
functions. 

The  fluids,  or  juices,  moving  in  the  vessels  of  plants, 
contain  the  nourishment,  and  constitute  the  essential 
means  by  which  food  is  assimilated  with  their  solid 
substances.  A  correspondence  is  thus  observable  be- 
tween their  functions,  and  the  circulation  of  the  blood, 
and  other  physiological  phenomena,  of  animals.  They 
possess  powers  of  motion,  irritability,  and  of  reproduc- 
tion ;  they  breathe,  sleep,  digest,  and  perspire.  Their 
peculiar  individual  character  is  preserved  by  their  vital 
functions,  which  constitute  their  life ;  and  when  they 
cease,  their  bodies  are  exposed  to  the  chemical  pro- 
cesses which  act  alike  on  all  inorganic  substances,  and 
they  die. 

"  See  dying  vegetables  life  sustain ; 
See  life,  dissolving,  vegetate  again." 

The  circulation,  or  motion,  of  the  juices  of  plants, 
is  thought  to  be  mechanical,  the  result  of  their  irrita- 
bility, the  vessels  acting  as  capillary  tubes,  &c.  This 
irritability  is  destroyed  by  shocks  of  electricity,  as  with 
animals.  Heat  and  light  greatly  increase  this  circula- 
tion, as  in  the  spring  of  the  year ;  while  cold  as  readily 
checks  or  suspends  it,  as  in  autumn  and  winter.  Long- 
continued  heat,  and  rapidity  of  circulation,  as  in  sum- 
mer, exhausts  their  power  of  irritability,  till  in  autumn 
it  is  slow,  and  their  fluids  are  thick,  as  in  animal  life, 
both  in  regard  to  season  and  old  age.  Their  repose, 
too,  after  the  activity  of  the  day,  and  their  revival  on 


EOT  AX  V.  309 

the  appearance  of  light,  are  not  less  remarkable  than 
with  man,  or  lower  animals,  under  like  circumstances. 

The  breathing  of  plants  is  their  absorption  and  ex- 
halations—  physiological  facts  as  notable  as  any  other 
in  the  vegetable  or  animal  economy.  This  is  per- 
formed by,  and  is  especially  observable  in,  the  leaves. 
A  plant  growing  under  ice  constantly  emits  bubbles 
of  pure  oxygen,  which  rise  to  escape.  Placed  also  in 
a  tumbler  of  water,  exposed  to  the  sun,  it  is  soon  seen 
to  be  covered  with  air-bubbles,  which  rise  to  the  sur- 
face and  burst  The  inspiration  of  carbonic  acid 
through  the  leaves  of  plants  is  as  constant,  and  in 
quantity  still  more  abundant  By  this  they  live  and 
furnish  their  organs  with  nourishment ;  and,  by  their 
expirations  during  the  day,  they  afford  the  vital  gaseous 
principle,  oxygen,  which  is  as  necessary  to  the  life  of 
man  and  the  animal  world  as  to  that  of  plants ;  with- 
drawing, at  the  same  time,  carbonic  acid,  which  is  most 
hurtful  to  animal  life.  Besides  gases,  they  also  exhale 
liquids,  which,  in  a  common-sized  tree,  amount  to  30 
pounds  a  day. 

Their  orfor,  thus  exhaled,  consists  of  volatile  oik, 
which,  in  quantity,  are  proportionate  to  their  volatility, 
their  nature,  light,  heat,  &c.  Their  taste  depends  on 
like  circumstances,  the  chemical  character  of  their 
constituents  and  the  nature  of  the  soil.  The  color  of 
plants  resides  in  their  cellular  substance,  beneath  the 
scarf  skin,  or  epidermis,  and  depends  on  the  peculiar 
functions  of  their  organs,  their  situation,  heat,  &c. 
Green  leaves  placed  in  the  dark  become  yellow,  and 
then  white.  Young  leaves  grown  in  the  dark  turn  from 
white  to  yellow,  and  then  to  green,  on  exposure  to 


310  BOTANY. 

light.  Blossoms  raised  in  the  dark  are  not  materially 
changed  by  light.  Plants  are  lighter  by  combining 
with  oxygen,  and  darker  on  parting  with  it.  Com- 
pletely saturated  with  it,  they  become  yellow,  as  with 
the  leaves  in  autumn  ;  but  under  other  circumstances, 
when  exposed,  they  turn  to  green.  The  light  of  a 
lamp  and  that  of  the  moon  produces  no  sensible  differ- 
ence in  effect. 

Secretions  and  excretions  are  likewise  remarkable 
functions  of  plants.  All  that  is  healthful  and  nutritive 
they  secrete  for  their  food  and  development,  and  all 
that  is  baneful  and  unproductive  they  reject  and  excrete 
through  their  roots.  These  withdraw  from  the  soil  its 
various  qualities,  which  constitute  their  life,  health,  and 
the  perfection  of  their  fruit ;  combining  and  assimi- 
lating all  that  is  essential  for  these  purposes,  and  cast- 
ing off  all  that  is  useless  or  poisonous,  yet  that  which 
may  be  eminently  useful,  nevertheless,  for  other  plants. 

The  existence  and  growth  of  plants  depend,  as  with 
animals,  on  the  reception  and  assimilation  of  food.  A 
knowledge,  therefore,  of  the  kind  of  nutriment  they 
require  is  of  great  importance  in  vegetable  physiology, 
as  well  as  in  practical  agriculture.  A  beautiful  re- 
lation is  thus  seen  between  the  organic  and  inorganic 
kingdoms.  Inorganic  matter  affords  food  for  plants, 
plants  afford  food  for  animals,  and  both  afford  food  for 
man.  Men  and  animals  require  substances  that  have 
life  and  organization ;  but  plants  require  inanimate  and 
inorganic  matter.  Both  are  apparent  machines  of 
greater  or  less  complexity,  each  depending  on  the 
other,  and  acting  to  produce  a  determinate  end. 

The  changes  produced  in  plants,  by  the  assimilation 


BOTAST.  311 

of  the  various  substances  of  which  they  are  composed, 
are  the  results  of  chemical  action,  and  are  traceable 
from  the  germ  to  the  full-grown  plant  and  fruit 
Water  and  carbon  are  resolved  into  their  constituent 
parts,  and  these  enter  into  new  forms  and  combinations, 
to  constitute  their  solid  portions.  The  hydrogen  of  the 
water  unites  with  the  carbon,  received  through  the 
leaves  from  the  air,  to  form  oils,  resins,  sugar,  <fcc. 
The  oxygen  of  the  water  combines  with  fluids  to  form 
acids,  &c.,  and  is  also  given  off  from  the  leaves  in  the 
form  of  gas. 

The  reproduction  of  plants  is  by  evolution,  which,  in 
process  and  effect,  is  similar  to  that  of  animals.  They 
are  endowed  with  organs  which  distinguish  sexes,  and 
which  are  generally  observable,  but  which  change  after 
evolution.  The  pollen  or  farina,  the  seminal  principle 
of  plants,  is  contained  in  vessels  called  anthers.  A 
part  of  this  penetrates  the  stigma*,  the  head  of  the 
pistil,  and  is  conveyed  to  the  ovary  of  particular 
plants,  and  there  the  germ  or  ovules  are  effected. 
Both  sexes  are  united  in  one  flower,  in  most  plants ;  in 
others  they  are  separated  ;  and  the  former  is,  therefore, 
called  a  perfect  flower,  while  the  latter  is  called  male 
and  female.  These  last  stand  on  one  stem,  or  are  at- 
tached to  different  plants.  Evolution  is,  consequently, 
most  perfect,  and  most  readily  effected,  in  the  perfect 
flowers,  as  they  are  called,  and  likewise  when  the  stem 
has  male  and  female  blossoms.  But  where  the  two 
sexes  are  entirely  separated,  evolution  takes  place  only 
where  the  plants  are  sufficiently  near  for  the  pollen  of 
one  to  be  carried  by  the  wind,  by  insects,  or  by  arti- 
ficial means,  to  the  other.  Should  this  not  take  place, 


312  BOTANY. 

the  germ  falls  off,  or  the  partial  fruit  is  incapable  of 
germination.  Glands  within  the  flowers  secrete  honey, 
and  attract  insects,  which  powder  parts  of  their  body 
with  pollen,  and  when  visiting  flowers  of  another  kind, 
they  deposit  it.  In  others,  it  is  said,  also,  where  per- 
fect flowers  of  the  two  sexes  are  not  near,  small  flies, 
being  attracted  by  the  honey  of  one  flower,  are  sud- 
denly ep'losed  by  it,  and  in  their  endeavors  to  escape, 
necessarily  deposit  the  pollen  obtained  from  other 
flowers.  On  this  system  of  sexes,  Linnseus  founded 
his  arrangement  of  plants. 

The  substances  of  plants  are  in  general  said  to  consist 
of  wood,  gum,  fecula  or  starch,  sugar,  gluten,  albumen, 
fibrine,  gelatin,  caoutchouc  or  India  rubber,  wax,  fixed 
and  volatile  oils,  camphor-resin,  gum-resin,  balsam,  ex- 
tract, tannin,  indigo,  acid,  aroma,  the  bitter,  the  acid 
and  narcotic  principles,  ligneous  fibre,  &c.  Many  of 
these,  however,  are  convertible  into  one  another,  by 
heat,  air,  moisture,  or  alkalies,  which  change,  more  or 
less,  the  relative  proportions  of  their  constituent?. 
Modern  chemistry  has  added  others,  or  arranged  the 
same  under  new  names  and  forms  of  combination,  and 
much  diminished  and  changed  the  terms  by  which 
vegetable  substances  have  been  known.  A  chemical 
analysis  has  proved  the  substances  to  be  carbon, 
oxygen,  hydrogen,  nitrogen,  sulphur,  silex,  oxide  of 
iron,  magnesia,  carbonate  of  lime,  potash,  &c. ;  and 
the  various  parts  of  plants  are  composed  of  these,  in 
different  proportions.  The  formation  of  substances 
composing  plants  is  the  result  of  chemical  operations 
during  their  growth  and  the  development  of  fruit. 
The  process  of  combining  the  original  elements,  their 
absorption  by  heat  and  light,  their  unition  in  various 


BOTANY.  313 

forms  and  combinations,  and  also  the  resolving  of 
original  substances  into  other  forms  and  compounds, 
constitute  more  especially  the  important  and  interesting 
science  of  organic  chemistry. 

Principles  of  plants.  The  proximate  principles  of 
plants  are  the  products  of  chemical  combinations  ef- 
fected by  the  action  of  the  vital  principle.  Such  are 
the  vegetable  acids,  wax,  resins,  the  fixed  and  volatile 
oils,  <Scc.  The  ultimate  principles  are  the  elements 
composing  the  proximate  principles,  as  carbon,  oxygen, 
and  hydrogen,  and  these  are  proportionate  to  the  nature 
and  quantity  of  these  elements.  Thus  those  substances 
composed  of  them  form  one  class  of  proximate  prin- 
ciples, and  those,  with  the  addition  of  nitrogen,  another 
class.  Those  of  the  one  class  have  an  excess  of  oxy- 
gen, (the  general  acidifying  principle,)  and  therefore 
constitute  the 

Vegetable  acids.  Acetic  acid,  or  pure  vinegar,  is 
commonly  produced  by  the  fermentation  of  wine 
cider,  &c. :  it  is  also  found  pure  in  the  elm.  Malic 
acid  may  be  obtained  from  green  «pples,  and  bar- 
berries. Oxalic  acid  is  found  in  a  species  of  the  sor- 
rel, or  the  genera  dxalis  and  rumex.  Tartaric  acid  is 
obtained  from  the  tamarind,  cranberry,  die. ;  and  when 
combined  with  potash,  forms  cream  of  tartar.  Citric 
acid  is  found  in  the  lemon,  and  is  mixed  with  the 
malic  acid  in  the  gooseberry,  cherry,  and  strawberry. 
Quinic  acid  is  obtained  from  the  Peruvian  bark. 
Gallic  acid  is  from  the  oak  and  sumach,1  and  is  very 
astringent  Benzoic  acid  is  found  in  the  laurus,  ben- 
zoin, and  vanilla;  it  is  highly  aromatic,  and  is  the 
agreeable  odor  of  balms.  Prussic  acid,  an  active 
xm.— 27 


314  BOTANY. 

poison,  is  obtained  from  peach  meats  and  blossoms, 
bitter  almonds,  cherry  leaves  and  meats. 

Gums,  sugar,  &c.,  compose  that  order  of  proximate 
principles  in  which  hydrogen  and  oxygen  are  in  the 
proportion  to  form  water.  These  unite  with  water,  but 
have  little  taste  or  smell.  They  compose  gum  arabic, 
the  common  gums  of  the  peach,  cherry,  and  other 
trees.  Sugar  is  from  the  sugar-cane,  maple-trees, 
beets,  corn-stalks,  pumpkins,  sweet  apples,  and  most 
vegetables  with  a  sweet  taste. 

Oils,  wax,  resins,  &c.,  in  which  hydrogen  is  in 
excess,  are  of  the  second  order  of  proximate  prin- 
ciples. They  do  not  unite  with  water.  Oils  are  fixed, 
as  oil  of  almonds,  olives,  flax-seed,  linseed  oil ;  and 
volatile,  which  have  aromatic  odors,  that  fly  off  when 
exposed  to  the  air,  as  the  oils  of  orange,  lavender, 
rose,  jasmine,  and  peppermint ;  and,  when  mixed  with 
alcohol,  they  form  essences.  The  aroma  is  the  volatile 
or  odoriferous  part  exhaled  from  aromatic  plants, 
especially  abundant  in  warm  climates.  Wax  is  found 
on  the  fruit  of  .the  bayberry ;  and  bees- wax  is  pro- 
duced by  bees  from  the  pollen  of  flowers.  Resins 
exude  from  the  pine,  &c. ;  they  are  insoluble  in  water, 
and  inflammable.  Mixed  with  volatile  oils,  they  form 
balsams,  which  are  thick  and  inflammable,  as  balsam  of 
tolu,  copayva,  &c.  When  mixed  with  gums,  they  are 
then  gum-resins,  as  gamboge,  guaiacum,  aloes,  assa- 
foetida,  &c.  Gum-elastic,  or  caoutchouc,  from  South 
America,  and  some  other  trees  of  the  tropics,  possess 
remarkable  properties.  The  juice  of  the  common 
milk-Aveed  is  said  to  be  similar  to  that  of  the  India  rub- 
ber plant.  The  valuable  properties  of  tbese  substances 


BOTAirr.  315 

would  form  the  subject  of  a  treatise  too  extensive  for 
our  limits. 

The  second  doss  of  proximate  principles  are  com- 
posed of  the  ultimate  elements  we  have  mentioned, 
with  nitrogen.  Such  are  opium,  the  narcotic  principle 
of  the  poppy  ;  hematine,  the  coloring  principle  of  Cam- 
peachy  wood ;  indigo,  from  species  of  the  indigo 
plant ;  gluten,  from  the  cotyledons  of  leguminous 
plants,  as  beans  and  peas,  also  from  the  albumen  of 
wheat,  rye,  &c.,  when  separated  from  the  starch. 
Jetty  is  the  juice  of  succulent  fruits,  as  apples,  quinces, 
currants,  <fcc.  The  coloring  principle  of  plants  gives 
to  them  their  green  color,  by  the  aid  of  light.  It  is 
changed,  as  in  autumn,  by  the  formation  of  an  acid. 
Thus  a  drop  of  an  acid  on  the  green  part  will  turn  it 
to  a  brown.  The  coloring  matter  of  some  plants  has 
never  been  obtained  separate  from  the  plant,  as  in  log- 
wood and  saffron.  The  red  coloring  of  fruit  is  pro- 
duced by  the  combination  of  an  acid  with  a  blue  color- 
ing principle,  as  an  acid  will  do  with  all  vegetable 
blues ;  this  is  deeper  in  proportion  to  the  quantity  of 
acid.  An  acid  with  iron  is  the  common  coloring  prin- 
ciple of  flowers. 

The  composition  of  the  sap  of  plants  is  from  the 
before-mentioned  elements,  and  water  holding  in  solu- 
tion the  earths  and  their  metallic  bases,  alkaline  salts, 
&c.,  with  vegetable  and  animal  substances.  It  is  not 
obtained  pure,  being  always  mixed  with  the  proximate 
principles  before  mentioned ;  and  it  differs,  hi  plants,  in 
proportion  to  those  principles.  The  power  or  property 
of  a  plant  to  secrete  one  kind  of  substance,  and  not 
another,  depends  on  its  constitutional  peculiarities,  as 


316  BOTANY. 

with  the  races  of  men  in  the  formation  of  their  differ- 
ent colors.  Water  is  always  a  predominant  constituent 
of  the  sap  of  plants.  An  analysis  of  the  sap  of  the 
elm  gives  water,  volatile  matter,  acetate  of  potash,  car- 
bonate of  lime,  sulphate  of  potash,  and  vegetable  mat- 
ter; of  the  beech,  water,  acetate  of  lime,  acetate  of 
potash,  gallic  acid,  tannin,  mucous  extract,  acetate  of 
alumina,  etc.  These  show  the  differences  in  the  ele- 
ments of  the  sap ;  they  also  differ  materially  in  their 
proportions.  The  odor,  taste,  nutritive  and  medicinal 
qualities,  color,  &c.,  are  all  the  result  of  these  ele- 
ments, variously  combined.  The  elements  are  the 
same  in  substances  of  very  different  character,  solids 
as  well  as  fluids ;  but  their  mode  of  combination  may 
form  vinegar  or  a  liquid  in  one,  and  sugar  or  a  solid  in 
another.  By  knowing  these  elements  and  their  pro- 
portions, similar  substances  may  be  produced  by  the 
chemist,  but  not  the  form  and  organization  of  the  plant, 
these  being  alone  the  work  of  nature,  in  conformity 
with  laws  established  by  Supreme  Wisdom. 

The  nourishment  of  plants.  Being  deprived  of  the 
powers  of  locomotion,  plants  must  have  organs  to 
obtain  their  food  from  the  situation  in  which  it  is 
placed,  and  also  for  assimilating  it.  This  food  is  in  a 
liquid  or  aeriform  state.  The  solid  particles  held  in 
liquids  must  be  in  a  very  fine  state,  as  commonly  dif- 
fused in  water  or  rain.  When  placed  in  water,  plants 
bloom,  but  the  nourishment  of  the  water  is  soon  ex- 
hausted. Distilled  water  has  lost  that  nourishment,  or 
its  carbonic  acid  gas,  &c.,  and  plants  soon  die  in  it. 

Spongelets  or  suckers,  like  the  organs  of  insects  that 
live  by  suction,  are  minute,  sponge-like  vessels,  on  the 


BOTANY.  317 

point  of  the  rootlets,  radicles,  or  small  fibres.  These 
pores  admit  only  of  fine  particles  dissolved  in  water ; 
otherwise  they  become  obstructed,  and  the  plant  per- 
ishes. The  pores  or  suckers  of  leaves  are  similar,  and 
perform  similar  functions. 

The  sap  vessels  are  congeries  of  fine  tubes,  straight 
and  curved,  forming  lace-work,  or  they  are  of  a  beau- 
tiful spiral  form.  The  straight  vessels  are  hollow 
threadlets,  fifty  times  finer  than  a  hair,  and  forming,  to- 
gether, large  tubes.  The  spiral  vessels  act  singly,  or 
in  bundles,  in  every  part  of  the  plant,  except  the  bark. 
The  circulation  through  these,  upwards  and  down- 
wards, is  exceedingly  curious.  The  organs  of  aera- 
tion are  not  like  those  of  the  lungs,  any  more  than  the 
pith  in  the  circulation  is  like  the  heart  of  animals ;  yet 
analogous  functions  are  performed  by  them  in  both. 
They  breathe,  and  it  is  by  the  air  they  are  chiefly 
nourished. 

Organs  of  sensation  in  plants.  It  has  been  thought 
by  some  that  plants  are  endowed  with  sensation,  senti- 
ments, and  propensities.  Nervous  organs  have  been 
disclosed,  it  is  said,  in  the  sensitive  and  other  plants. 
There  is,  at  the  base  of  the  leaf-stalk  of  this  plant,  a 
swelling  collar,  constituted  of  a  delicate  tissue  of  cells, 
on  which  the  motion  of  the  leaves  depends.  The  under 
part  being  cut  away,  the  leaf  bends  down,  and  cannot 
again  rise;  and  the  upper  part  being  cut,  it  cannot 
bend.  These  are  acted  on,  it  is  believed,  by  nervous 
globules,  or  grains,  or  ganglia,  as  diffused  in  all  plants 
by  medullary  vessels.  The  effects  of  experiments  cer- 
tainly show  an  analogy  between  plants  and  animals, 
but  nothing  more.  Leaves  and  flowers  turn  to  the  light 
27* 


when  twisted  ;  these  curl  up  and  die  when  watered 
with  poisons.  Twining  plants  twine  from  right  to  left, 
or  left  to  right,  according  to  species. 

The  existence  of  plants  has  been  compared  to  that 
of  animals  when  asleep,  their  functions  proceeding 
during  the  time  without  consciousness.  A  seed  placed 
in  the  earth  is  similar,  in  its  nature,  to  the  egg  uT  an 
animal ;  and  the  effects  of  the  earth  would  seem  not 
unlike  that  of  sitting  upon  it,  or  the  development  of  the 
young  of  amphibious  animals  with  the  egg  covered  by 
the  earth.  It  is  obviously  very  difficult  to  determine  at 
what  point  vegetable  life  ends  and  animal  life  begins. 
The  sponge  is,  in  many  respects,  less  sensitive  than 
some  plants,  yet  it  is  ranked  among  animals  ;  and  so 
also  with  corals.  Although  we  might  show  how 
plants  grow,  yet  it  may  not  appear  plain  how  they  live. 
They  live,  it  is  true,  like  animals,  by  the  food  they 
receive  and  assimilate ;  yet  the  generation  of  the  vital 
principle  which  constitutes  life  is  not  explained.  By 
observing  the  facts  which  are  hereafter  stated,  it 
will  be  seen  that  there  are  clear  distinctions  between 
the  animal  and  vegetable  kingdoms,  notwithstanding 
the  analogies  of  life  we  have  noticed. 

Age  of  plants.  Many  small  funguses,  called 
moulds,  live  but  a  few  hours,  or  not  longer,  at  most, 
than  a  few  days.  Garden  plants  and  mosses  live  but 
one  season,  dying  of  old  age  as  soon  as  they  ripen  their 
seeds.  Others  live  two  years,  and  sometimes  three,  if 
their  flowering  is  prevented,  such  as  the  fox-glove  and 
hollyhock.  These  are  the  annual  and  biennial  shrubs, 
herbs,  &c.  Many  live  not  only  through  the  winter,  but 
are  perpetually  or  perennially  green.  Such  are  ever- 


BOTANY.  319 

greens  or  forest  trees.  These  live  oftentimes  for 
many  centuries,  producing  annually  new  leaves.  Thus 
the  olive,  vine,  oak,  cedar,  and  chestnut,  live  300,  and 
even  1000  years.  The  dragon's-blood  of  TenerifFe  is 
estimated  to  be  2000,  or  more,  years  old  ;  and  the 
banian  may  be  6000.  The  interior  of  trees  often  be- 
comes too  compact  for  the  sap  to  circulate,  or  for  the 
formation  of  new  vessels ;  its  moisture  passes  into 
younger  wood,  and  the  fibres  shrink  and  become  pow- 
der ;  but  the  outer  parts  live,  and  the  tree  survives, 
even  for  centuries. 

Laics  and  vital  principles.  Inorganic  matter  is  the 
medium  through  which  organic  matter  derives  its  or- 
ganization and  vitality.  This  matter,  in  its  ordinary 
state,  undergoing  neither  the  process  of  organization 
nor  of  decomposition,  belongs  especially  to  the  mineral 
kingdom.  From  this,  then,  the  vegetable  kingdom 
mainly  derives  its  powers ;  and  from  the  vegetable 
kingdom  are  derived  those  of  the  animal  kingdom.  It 
is  only  when  animal  and  vegetable  substances  have 
been  deprived  of  vitality,  and  are  no  longer  subject  to 
the  laws  of  organic  matter,  but  have  become,  by  death, 
subject  to  the  laws  of  inorganic  matter,  that  vegetables 
are  in  part  supported  by  them.  But  animals  are  sup- 
ported by  organic  matter,  or  that  which  has  had  vitality, 
and  before  the  laws  of  inorganic  matter  have  operated 
upon  it.  It  will  be  perceived  that  inorganic  matter,  or 
that  of  the  mineral  kingdom,  possesses  the  same  prop- 
erties, when  divided  or  ground  to  powder,  that  it  does  in 
the  mass ;  i.  e.  each  particle  possesses  those  properties 
in  proportion  to  its  size  •,  while  the  organic  parts  of 
animals  or  of  vegetables,  if  thus  crushed  or  divided, 


are  deprived  by  death  of  the  vital  forces  which  distin- 
guished them  from  inorganic  matter. 

The  seed  of  a  plant,  if  placed  in  the  earth,  forms  a 
living  plant,  which,  from  its  incipiency,  opposes  inor- 
ganic laws,  or  those  of  decomposition.  The  vital  prin- 
ciple which  it  has  received  from  the  seed,  and  which 
the  seed  has  parted  with,  together  with  a  portion  of 
its  substance,  for  its  suppoi't,  continues  to  animate  the 
plant ;  while  the  remainder  of  the  seed  has  thereby 
become  subject  to  the  inorganic  laws,  and  rots,  or  is 
decomposed  in  the  ground.  The  plant  lives  and  flour- 
ishes ;  and,  by  the  force  of  its  vital  powers,  thus  ob- 
tained, appropriates  inorganic  matter  to  its  support  and 
the  development  of  its  organs,  until,  by  violence  or  the 
exhaustion  of  its  vital  energies  at  maturity,  it  is  at 
length,  and  in  turn,  subjected  to  the  force  of  the  inor- 
ganic laws ;  it  dies,  and  is  decomposed,  either  in  the 
ground  or  by  being  consumed  by  animals.  The  seed 
originally  derived  its  vital  principle  from  its  parent 
plant,  through  its  pericarp,  or  fruit,  and  retained  it  within 
its  envelopes  until  buried,  and  excited  to  germination  by 
the  heat  and  moisture  within  the  earth,  when  it  gave  it 
to  its  offspring. 

During  the  period  from  the  birth  to  the  death  of  a 
plant,  periods  of  repose  intervene,  as  with  biennial  and 
perennial  plants  in  winter.  It  loses  its  leaves,  the 
principal  means  of  its  support,  and  remains  partially 
dormant,  until  awakened  to  action  by  the  heat  of  re- 
turning spring,  when  its  leaves  are  renewed,  and  its 
dormant  energies  call  forth  new  shoots,  buds,  and 
blossoms,  and  the  scene  of  life,  health,  vigor,  and 
action,  is  reenacted. 

Light  is  evidently  one  of  the  "  necessaries  of  life,'7 


and  plays  an  important  part  in  vegetation  and  the 
economy  of  plants.  By  it  they  form  their  combustible 
parts.  The  carbon  they  receive  must  be,  in  some  way, 
modified  by  its  influence  before  it  can  become  a  con- 
stituent of  the  plant.  During  the  night,  they  probably 
do  little  more  than  to  digest  the  food  they  have  received 
during  the  day,  and  to  separate  and  give  off  that  which 
is  not  found  nutritious.  Light  is  a  primary  agent  from 
the  time  the  plant  emerges  from  the  soil  to  its  death. 
Its  nature  becomes  changed  by  its  absence,  so  that  the 
observer  would  scarcely  recognize  its  identity  by  its 
form,  color,  taste,  or  odor.  If  a  branch  of  any  spread- 
ing plant  penetrates,  in  its  growth,  a  subterranean  place, 
its  character  becomes  not  only  thus  changed,  but  it  is 
found  composed  almost  entirely  of  water,  and  assumes 
the  nature  of  a  fungus,  so  that  all  of  its  native  beauties 
and  virtues  are  lost ;  it  is  a  mere  pulp  deprived  of  its 
resinous  qualities.  The  acid  taste  of  some  vegetables, 
as  the  endive  and  celery,  may,  however,  be  corrected 
by  bleaching. 

Diseases  of  plants.  These  arise  from  many  causes, 
as  with  man  and  lower  animals.  They  may  be  de- 
tected and  cured  by  a  careful  observance  of  the  nature 
and  wants  of  plants.  The  change  in  the  color  of  the 
leaves  of  the  box  and  holly  is  said^  to  be  a  disease,  or 
disordered  condition,  of  the  juices.  Too  much  or  too 
little  food,  or  that  which  is  poisonous,  produces  dis- 
eases. Too  little  or  too  much  light,  heat,  air,  water, 
and  soil,  an  excess  of  light,  so  as  to  cause  the  escape 
of  too  much  oxygen,  or  too  rapid  a  deposit  of  carbon, 
are  also  causes  of  disease.  By  a  knowledge  of  the 
properties  and  characteristics  of  plants,  we  may  per- 
TJ 


ceive  their  wants,  and  frequently  apply  remedies 
adapted  to  their  diseased  condition.  Their  health  is 
often  affected  by  external  injuries.  Rains  and  winds 
also  injure  them,  oftentimes.  Smoke  obstructs  the 
pores  of  the  leaves,  and  is  thereby  greatly  prejudicial. 
Animals  are  a  frequent  cause  of  disease  in  plants. 
Some  penetrate  the  bark,  and  deposit  their  eggs,  pro- 
ducing larvae,  and  the  insect  cynips.  By  one  kind  of 
fhese,  protuberances  are  produced,  as  the  nutgall  of 
oaks,  apple  or  berry  galls.  Some  prey  on  the  juices, 
as  with  the  insect  cochineal,  a  species  of  which  is  so 
valuable  for  dyeing  a  scarlet  color.  The  Mexican  plant 
cactus  cochinilifer  is  that  which  they  feed  upon.  Dis- 
ease is  likewise  produced  by  contiguity  with  other 
plants,  either  by  ejecting  deleterious  matter  from  their 
roots,  or  withdrawing  that  which  is  necessary  for  one 
or  the  other.  Mosses  and  lichens  attach  themselves  to 
trees,  and  absorb  moisture,  or  attract  insects,  both  of 
which  destroy  the  wood ;  they  do  not,  however,  feed 
on  the  juices,  and  are,  therefore,  called  false  parasites, 
The  mistletoe  pierces  the  bark  and  feeds  on  the  juices, 
and  is  a  true  parasite.  Another  parasite,  called  the 
pterospora,  is  found  on  the  leaves  and  branches  of 
trees.  Smut  and  rot  are  fungi,  the  former  fastening 
itself  on  the  ears  o£  cereal  grains,  and  the  latter  prey- 
ing on  the  seeds.  If  these  seeds  be  planted,  the  dis- 
ease will  be  continued  in  the  plant.  Rust  and  ergot 
are  also  fungi,  the  one  a  disease  of  rye,  and  the  other 
of  grasses.  As  plants  renew  their  parts  annually,  they 
seem  less  liable  to  be  affected  by  old  age  ;  still  their 
powers  of  renewal,  or  vital  principle,  become  ex- 
hausted in  time,  as  with  animals.  In  annual  olants, 


the  production  and  maturing  of  fruit  exhaust  their 
energies  during  the  year,  and  in  biennials  in  two  years. 
These,  however,  as  with  perennials,  depend  much  on 
their  constitution  and  the  amount  of  their  fruit,  as  with 
the  apple-tree,  which,  being  very  fruitful,  does  not 
often  attain  to  so  great  an  age  as  the  oak,  the  fruit  of 
which  is  light. 

The  effects  produced  by  insects  on  plants  are  vastly 
greater  than  in  producing  deformities.  Like  great 
fires,  however,  they  may  often  prove  a  benefit,  and 
maintain  a  balance  among  the  various  species  of  plants ; 
/or  the  devastating  effects  of  these  insignificant  agents 
are  wonderful.  Scarcely  a  plant  is  without  one  or 
more  species  of  insect  The  diseases  they  produce 
often  constitute  an  important  article  of  food,  medicine, 
and  commerce,  as  we  have  said,  in  the  cactus,  or  coch- 
ineal insect ;  the  lac  insect ;  the  cantharia,  or  Spanish 
fly ;  the  gall  apples,  and  the  nut  galls. 

The  sweeping  destruction  produced  by  the  locust 
affords  a  striking  discrepancy  between  the  magnitude 
of  the  means  and  that  of  the  effects.  They  can  strip 
entirely  of  their  foliage  thousands  of  square  miles  of 
forest-trees  during  one  brief  visit,  and  annihilate  every 
appearance  of  vegetation ;  as  when  they  thus  scourged 
Masinissa,  causing  the  death  by  famine  of  more  than 
800,000  persons !  Compared  with  such  effects,  earth- 
quakes and  volcanoes  dwindle  into  insignificance. 

Their  numbers  are  so  vast  as  often  to  overshadow 
immense  tracts  of  country.  The  swarm  which  passed 
over  Smyrna,  like  a  living  cloud,  for  three  days  and 
nights,  was  calculated  to  be  900  feet  deep,  more 
than  40  miles  wide,  and  50  miles  in  length!  The 


number  exceeded  168,608,563,200,000,  and  the  mag- 
nitude of  the  mass,  if  gathered  into  a  heap,  would 
exceed  by  more  than  1030  times  that  of  the  largest 
pyramid  of  Egypt,  or  would  encircle  the  whole  earth 
with  a  belt  a  mile  and  a  furlong  wide.  When  borne 
down  by  tempests,  their  bodies  have  overspread  large 
tracts  of  country  4  feet  deep,  or  formed,  when  thus 
driven  into  the  sea,  windrows  along  the  shore  3  or  4  feet 
deep,  for  50  miles  in  extent ! 

The  aphides,  or  rose  bugs,  the  flies  of  the  turnip 
fields,  and  the  timber  grubs,  are  also  terribly  destruc- 
tive. The  "great  goat  moth"  is  likewise  a  powerfully 
destructive  insect  to  plants.  Its  larvae  are  proved 
to  increase  their  weight  140  times  within  an  hour,  and, 
when  full  grown,  are  72,000  times  heavier  than  when 
hatched !  The  termes  lellicosus  lays  sixty  eggs  per 
minute,  and  continues  to  do  so,  without  interruption,  for 
an  incredible  time  ;  thus  laying,  it  is  calculated,  3600 
eggs  per  hour,  or  86,400  per  day!  The  common 
flesh  fly,  it  is  said,  will  give  birth  to  20,000  young ; 
and  the  three  flies,  musca  vomitoria,  Linnseus  and 
others  have  said,  can  devour  a  dead  horse  as  quick  as 
a  lion,  or  commit  more  ravages  than  an  elephant. 
They  are  thus  important  scavengers.  The  pine  forests 
of  Germany  have  sustained  immense  injuries  from  a 
small  beetle,  which  has  deposited  80,000  larva?  in  one 
tree.  Preying  on  the  inner  bark,  they  have  thus  de- 
stroyed, in  one  forest,  1,500,000  trees,  and  then,  on 
maturity,  taken  wing,  and  flown  to  other  forests  with 
like  results.  It  was  a  subject  of  great  wonder  at  one 
time,  in  London,  how  the  elm-trees  in  some  of  the 
parks  became  completely  stripped  of  their  bark.  Sus- 


pecting  it  to  be  caused  by  soldiers,  many  were  arrested, 
and  watches  stationed  to  secure  the  depredators ;  still 
the  work  of  destruction  ceased  not.  Various  other 
causes  were  supposed,  and  severe  measures  taken  to 
punish  the  culprits ;  until,  at  length,  they  were  found 
to  be  no  others  than  insects,  which  were  ultimately 
checked  in  their  career  by  art. 

The  economy  of  plants,  as  observed  in  their  habits, 
is  strikingly  illustrative  of  the  harmony  of  nature. 
We  see  them  adapted  to  the  peculiarities  of  their  situ- 
ations. If  indigenous  to  the  tropical  climate,  they 
cannot  live  in  our  temperate  zone  without  the  aid  of 
art ;  if  inhabitants  of  the  valley,  they  cannot  dwell  on 
the  mountain's  summit;  nor,  if  the  rugged  tenants 
of  the  bleak  and  frosty  mountain,  can  they  endure  the 
enervating  dalliance  of  the  luxurious  vale  ;  nor  can 
either  dwell,  with  the  aquatic  plant,  immersed  in  a  liquid 
element.  We  have  noticed  many  of  the  habits  of 
plants ;  and,  in  many  ways  which  we  cannot  particu- 
larly notice,  they  minister  to  our  wants  as  food,  clothing, 
medicines,  in  the  arts,  and  to  the  support  of  inferior 
animals.  The  interest  with  which  they  must  be 
viewed,  with  their  numberless  shoots  urging  into  life 
and  action  their  millions  of  buds,  that  are  expanded 
into  light  and  being  by  the  genial  sun,  rivalling  one 
another  in  their  efforts  to  produce  the  fairest  flower, 
and  choicest  fruit,  —  these  render  them  objects  of 
peculiar  attention.  But  a  change  comes  over  them, 
as  we  have  seen,  and  as  we  daily  witness  with  fellow- 
mortals.  They  die  and  mingle  with  the  soil,  and  from 
their  decomposed  remains  spring  up  new  beings. 

The  various  forms  of  plants,  in  this  connection,  can- 
XIIL — 28 


not  fail  to  strike  us  with  wonder.  Although  this  is 
remarkable  in  the  100,000  different  species  of  insects, 
yet  the  variations  are  not  so  obvious  in  the  range  of 
such  minute  objects  as  in  plants,  nor  are  they  more  pro- 
lific in  wonders.  In  every  situation  capable  of  sustaining 
life  we  find  plants  arise,  and  continue  their  species  in 
endless  perpetuity.  The  germs  are  every  where  found 
where  the  soil  is  upturned,  and  where  they  may  have 
remained  dormant  perhaps  for  centuries.  Islands 
formed  of  coral  reefs,  and  even  sterile  rocks,  cinders, 
and  lava  of  recent  volcanoes,  are  found  covered  with 
vegetable  forms.  The  germs  that  float  invisibly  in  the 
air  successively  follow  each  other,  and  plant  the  most 
barren  places  with  verdure,  which,  rising  from  grasses 
to  shrubs,  and  from  shrubs  to  trees,  soon  present  all 
the  varied  forms  of  meadows,  thickets,  and  forests. 
Thus,  considered  in  reference  to  their  utility,  the 
beauty  of  their  forms  and  colors,  their  fruit  and 
fragrance,  or  the  continuation  of  their  species,  they 
forcibly  impress  us  at  all  times  with  admiration  and 
delight. 

The  utility  of  plants  is  unbounded  and  illimitable. 
Nowhere  do  they  rise  in  vain.  The  lofty  tree,  what- 
ever its  intrinsic  properties,  presents  its  cooling  and 
refreshing  shades  for  flocks  and  herds,  and  offers  an 
asylum  for  the  insect  tribe,  and  for  the  songsters  of  the 
air.  As  food,  the  bread-fruit  tree  of  the  Pacific,  and 
the  cabbage-tree  of  our  own  and  other  southern 
climes,  the  sugar-maple  of  the  United  States,  the  tea- 
tree  of  China,  the  sugar-cane,  the  cotton-shrub,  and 
the  coffee-tree,  and  the  innumerable  fruit-trees,  which 
every  where  yield  in  rich  profusion  their  varied  prod- 


ucts  ;  the  fountain-tree  of  the  Canaries,  that  yields  pure 
water;  the  tallow-tree  of  China;  the  mulberry-tree, 
nourishing  myriads  of  beings  that  industriously  supply 
us  with  silks ;  the  salt- tree  of  Chili,  that  daily  supplies 
the  people  with  salt ;  the  cinnamon,  pimento,  and 
clove,  that  furnish  our  spices  ;  the  Peruvian  bark,  the 
senna,  manna,  and  innumerable  other  medicinal  plants ; 
those,  too,  yielding  their  healing  balsams,  turpentine, 
resins,  oils,  and  gums, —  all,  all  furnish  us  with  their 
invaluable  products.  Nor  are  they  less  important  in 
protecting  us  by  the  buildings  we  raise  with  them,  or 
in  the  conveniences  and  luxuries  they  afford  us  by  the 
ships  we  build  of  them  to  transport  the  products  of  one 
clime  and  people  to  those  of  another. 

Shrubs  and  herbs  also  supply  us  with  every  variety 
of  food  and  useful  product  There  the  golden  wheat 
presents  its  abundant  crops,  and  here  the  flowing  oats 
and  potatoes,  the  loaded  pea,  the  swelling  turnip,  beet, 
and  carrot,  the  luxuriant  grass  and  bountiful  com, 
crown  the  earth's  surface  with  life  and  nourishment ; 
while  the  universal  smiles  of  variously-tinted  flowers 
invite  us  abroad  to  view  the  charms  and  inhale  the 
odors  of  their  fragrant  breath.  All  here  spread  out 
before  us  the  rich  bounties  and  varied  delights  of  vege- 
table nature.  Well  may  it  be  said,  with  all  these  in 
view,  that  "  In  reason's  ear  they  become  preachers." 

CLASSIFICATION  OF  PLANTS. 

According  to  the  latest  researches  of  naturalists, 
about  80,000  plants  of  distinct  specific  forms  have  been 
discovered  ;  but  it  is  believed  that  as  many  more  remain 
to  be  made  known,  and  additions  to  the  list  are  con- 
stantly taking  place.  For  the  sake  of  order  and  classi- 


fication,  as  in  the  case  of  the  animal  kingdom,  all 
plants,  from  the  lowest  to  the  highest  forms  of  vege- 
tation, are  arranged  in  a  progressive  series  of  groups 
or  families,  the  members  of  which  possess  a  common 
resemblance,  or  are  otherwise  allied  in  character.  Ac- 
cording to  the  Linnsean  system,  the  whole  vegetable 
kingdom  is  arranged  in  two  grand  divisions  —  namely, 
Phcenogamia.,  plants  having  visible  flowers,  and  Cryp- 
togamia,  plants  having  no  visible  flowers.  The  whole 
are  also  divided  into  classes,  orders,  genera,  and  spe 
cies,  each  species  containing  a  number  of  varieties. 

LOWER  FORMS  OF  VEGETATION.  —  CRYPTOGAMIA. 
Among  these  are  included  the^/wngi,  the  musci,  (mosses,) 
hepaticce,  (liverworts,)  lichines,  (lichens,)  alga,  (sea- 
weeds,) andj/iZices,  (ferns,)  &c. 


Fungi.  These  may  be  placed  at  the  very  bottom 
of  the  vegetable  scale,  and  are  observable  in  a  great 
variety  of  forms,  and,  among  others,  mushrooms,  toad- 
stools, puflf-balls,  the  fungous  dryrot,  fermentation, 
mildew,  and  mould.  These  afford  a  most  interesting 
topic  of  discussion ;  but  we  have  room  only  to  name 
them. 


329 


Alga.  It  is  generally  allowed  that  these  embrace 
the  most  minute  forms  of  vegetation  not  of  a  fungous 
character.  One  of  these  forms  is  that  which  has 
vulgarly  been  called  red  snow,  or  bloody  rain.  A 
shower  of  red-colored  rain  or  snow  is  by  no  means  a 
rare  phenomenon  in  the  northern  parts  of  Europe,  or 
within  the  arctic  circle  ;  and  the  tinging  matter,  which 
has  been  accurately  examined,  is  found  either  to  pro- 
ceed from  the  incorporation  of  vegetables  or  animal- 
cules, both  too  small  to  be  seen  by  the  naked  eye. 
The  coloring  vegetable  matter  is  an  aggregation  of  an 
infinitude  of  plants  either  sucked  up  by  a  water-spout 
into  the  atmosphere,  or  overtaken  while  carried  along 
by  the  winds,  and  brought  down  by  the  falling  drops. 
On  the  stones  by  the  side  of  brooks,  we  may  some- 
times observe  a  similar  reddish  coloring  matter,  which, 
if  not  caused  by  metallic  ores,  will  generally  be  found 
to  be  a  primitive  kind  of  vegetation.  When  touched,  it 
feels  slippery,  and  on  examination  by  a  microscope,  it 
is  observed  to  contain  myriads  of  plants,  each  consist- 
ing of  a  small  vesicle  or  globule,  which,  on  arriving 
at  maturity,  expands,  bursts,  and  liberates  germs  of  its 
own  species.  This  excessively  humble  plant  is  classed 
28* 


330  BOTANY. 

with  the  algse,  as  being  the  nearest  to  it  in  character, 
although  these  plants  are  for  the  most  part  of  a  large 
size,  and  grow  principally  on  rocks  in  the  sea. 

The  object  which  nature  has  in  view  by  the  germi- 
nation and  dispersal  of  the  algse,  mosses,  and  lichens, 
is  clearly  that  of  preparing  the  way  for  other  plants, 
destined  to  subserve  important  purposes  in  the  circle 
of  nature. 

HIGHER  FORMS  OF  VEGETATION.  —  PH.ENOGABIIA. 
We  now  ascend  to  the  second  great  division  in  the 
vegetable  kingdom,  containing  plants  which  flower, 
and  possess  the  attributes  of  distinct  seeds,  roots, 
stems,  branches,  and  leaves. 

Seeds  are  the  offspring  of  plants.  They  are  dis- 
charged spontaneously  from  the  parent,  and  such  is 
the  care  that  nature  has  taken  for  their  preservation, 
that  many  of  them  will  remain  uninjured  for  centuries, 
till  a  favorable  opportunity  is  presented  for  their  de- 
velopment. They  contain  a  vital  principle  or  embryo, 
which  is  in  all  respects  like  the  parent,  unless  art  has 
interfered  to  change  its  form  or  qualities.  When 
seeds  are  ripe,  they  are  shed  from  the  capsules,  or 
from  the  other  parts  to  which  they  are  attached,  and 
are  then  covered  with  one,  two,  or  three  integuments, 
to  preserve  them  till  the  season  arrives  when  other 
favorable  circumstances  conspire  to  produce  germina- 
tion. A  perfect  seed  is  one  of  the  most  wonderful 
productions  in  nature !  It  contains  a  living  principle 
within  an  organized  body  of  cellular  membrane,  capa- 
ble of  indefinite  expansion.  When  placed  in  the  earth, 
by  the  influence  of  heat  and  moisture  expansion  takes 
place,  the  outer  covering  is  burst  asunder,  the  root 


descends  in  searcn  of  food  and  moisture,  and  the  stalk 
then  ascends,  to  put  forth  its  various  members  of 
branch,  leaf,  and  flower. 

The  general  form  of  seeds  is  kidney-shaped  :  some 
are  provided  with  appendages  for  defence  ;  others  with 
little  hooks  or  wings,  to  assist  their  dispersion.  The 
various  means  employed  by  nature  for  the  scattering 
of  seeds,  such  as  winds,  rivers,  rains,  birds,  animals, 
and  man,  afford  a  striking  instance  of  that  far-seeing 
wisdom  which  characterizes  the  great  Legislator  of  the 
universe.  All  seeds  are  enclosed  in  a  thin  fibre  of 
cellular  tissue,  and  many  are  further  protected  by 
pods  and  shells.  Some  are  covered  with  a  pulpy 
*r  a  fleshy  substance,  constituting  many  of  our  deli- 
cious fruits,  such  as  pears,  apples,  plums,  cherries, 
peaches,  &c. 


The  root  is  at  first  a  spear-shaped  body,  descending 
directly  downward  into  the  earth,  either  avoiding  the 
light,  or  seeking  the  moisture.  It  soon  throws  off 
small  fibres  from  its  point  and  along  its  sides.  These, 
in  their  turn,  throw  off  branches  and  fibres  — the  whole 
process  being  continued  so  long  as  the  plant  above 


requires  it.  The  fibres  are  the  real  mouths  by  which 
the  moisture  and  nutriment  of  the  plant  are  received. 

The  trunk  or  axis  of  a  plant  is  that  columnar  body, 
which,  if  above  ground,  serves  to  support  and  elevate 
the  fructification.  It  assumes  many  forms  and  char- 
acters, as  to  bulk,  structure,  position,  place,  and  dura- 
tion. It  appears  as  a  tuber,  a  bulb,  a  scape,  a  culm,  or 
as  a  woody  column.  It  varies  in  size  from  that  of  a 
bristle  to  a  trunk  of  many  feet  in  diameter.  In  structure, 
stems  are  hollow  or  solid,  jointed  or  simple,  single  or 
numerous.  In  position,  they  are  erect,  inclining,  pros- 
trate, or  involving.  They  rise  in  the  air,  creep  on  the 
surface,  or  enter  deep  into  the  ground.  They  are 
succulent  or  woody :  if  the  former,  they  are  quickly 
perishable ;  if  the  latter,  they  are  more  or  less  durable. 

The  pith  occupies  the  centre  of  the  stem,  and  con- 
stitutes the  principal  part  of  the  bulk  of  the  seedling, 
and  of  every  young  shoot.  It  is  more  or  less  filled 
with  a  spongy  matter,  easily  permeable  by  fluids. 
There  seems  to  be  no  action  in  the  pith,  except  as  a 
duct,  after  the  first  year  ;  for,  as  it  increases  in  age,  it 
decreases  in  volume,  and  in  old  trees  becomes  almost 
obliterated. 

Of  the  wood.  The  first  layer  of  this  principal 
member  of  a  stem  is  simultaneously  produced  with  the 
pith  which  it  surrounds.  During  its  growth  it  appears 
in  three  different  states  ;  at  first,  it  is  like  thin,  colorless 
jelly,  in  which  state  it  is  called  cambium;  next,  it 
gains  a  substance  like  gum,  showing  faint  signs  of  or- 
ganization ;  and  lastly,  as  perfect  wood,  called  albur- 
num, having  all  the  fibrous  structure,  cells,  tubes,  and 
consistence,  of  timber.  In  this  manner,  the  diameter  of 


all  dicotyledonous  stems  are  annually  enlarged  by  con- 
centric layers,  the  pith  being  in  the  centre  of  the  whole. 
These  layers  of  wood  are  composed  of  a  mass  of  ligne- 
ous fibres,  closely  and  longitudinally  arranged,  extend- 
ing from  the  base  to  the  summit  of  the  trunk,  and  to 
that  of  every  branch  of  the  spreading  head.  The 
fibres  are  imbedded  in  dense  cellular  matter,  the 
cells  of  which  are  placed  horizontally  between  the 
bundles,  and,  being  distended  in  the  line  of  their  posi- 
tion, give  thickness  to  the  alburnous  layer. 

The  number  of  the  layers,  reckoning  from  the  pith 
to  the  bark,  on  one  side  of  a  transverse  section  of  the 
butt  or  trunk,  indicates  the  age  of  the  tree  exactly ;  for 
the  layers  never  run  into  each  other,  nor  do  they  in- 
crease or  diminish  after  they  are  once  imposed. 

After  the  tree  has  passed  its  mature  age,  it  at  last 
begins  to  decay  ;  the  first  imposed  layers  next  the  pith 
fail  first;  and  this  decay  at  the  heart  extends  out- 
wardly, till  the  trunk  becomes  a  hollow  cylinder,  when 
the  whole  is  laid  prostrate  by  the  wind.  This  happens 
sooner  or  later,  according  to  the  durability  of  the  tim- 
ber. Some  kinds,  from  the  light,  porous  character  of 
the  wood,  and  aqueous  quality  of  the  sap,  perish  in  a 
few  years ;  others,  from  the  density  of  the  grain,  and 
preservative  quality  of  its  concreted  juices,  resist  decay 
for  many  years. 

The  stalk  of  the  seedling  rises  from  the  ground  with 
its  coat  of  bark,  consisting  of  a  layer  of  green  matter, 
covered  by  a  thin  cuticle.  This  ever  remains  on  the 
exterior  of  the  greater  number  of  trees,  and  is  distended 
as  the  internal  growth  increases.  Some  few  trees  and 
shrubs  discharge  their  bark  every  third  or  fourth  year ; 


334  BOTANY. 

but  on  the  greater  number  the  outer  bark  remains,  and 
is  either  rent  into  longitudinal  irregular  furrows,  or 
stretched  horizontally.  At  the  end  of  the  second  year, 
the  second  layer  of  bark  within  the  first  becomes 
visible,  and  takes  the  name  of  liber,  a  new  layer  of 
liber  being  formed  within  the  former  in  every  year 
during  the  -life  of  the  tree.  The  diameter  of  the  tree 
is  thus  increased  by  a  new  layer  of  alburnum,  or  white 
wood,  and  a  new  layer  of  liber. 

Branches  are  only  subdivisions  of  the  trunk,  being 
quite  similar  in  structure.  They  differ  much  in  the 
manner  of  their  divergence,  being  mostly  irregular, 
and  spreading  obliquely  forward.  Others,  as  the  pine 
tribe,  are  regularly  branched  from  bottom  to  the  top  in 
annual  growths ;  the  stem  rising  erect,  and  the  branches 
stretching  out  horizontally  in  every  direction. 

Leaves  are  the  grand  ornaments  of  plants ;  from 
their  numbers,  position,  and  delicacy  of  organization, 
they  are  destined  to  effect  some  important  office  in  the 
economy  of  the  plant.  They  are,  however,  only  tem- 
porary organs,  being  articulated  with  the  surface  of  the 
bark,  and  always  seated  upon  or  near  the  buds.  Those 
of  deciduous  trees  or  shrubs  drop  or  wither  as  soon  as 
the  summer  growth  is  over.  Some  of  both  of  those 
descriptions  retain  their  leaves  to  the  second  or  third 
year ;  hence  they  are  called  evergreen ;  and  some  of 
the  pines  and  firs  retain  them  for  many  years. 

The  web  of  the  leaf  is  filled  up  between  the  veins 
by  cellular  tissue,  having  a  thin,  porous  cuticle  both 
above  and  below.  The  structure  of  the  upper  ar.d 
under  surfaces  of  the  leaves  is  not  alike  ;  one  is  sup- 
posed to  be  furnished  with  excretory,  and  others  with 


incretory  organs.  Water  plants,  whose  leaves  are 
constantly  submersed,  have  no  cuticle. 

Of  the  flower  and  fructification.  The  members  of 
the  flower  are  the  calyx,  corolla,  stamen,  disk  or  necta- 
rium,  pistillum,  and  receptacle.  The  calyx  is  the  exter- 
nal investment  of  the  flower,  and  in  which  it  sits  as  in 
a  cup.  The  corolla  is  the  delicate  and  usually  high- 
colored  row  of  leaves  or  petals  which  stand  imme- 
diately within  the  calyx. 

The  stamens  are  placed  within  the  corolla,  and  are 
the  male  parts  of  the  flower,  consisting  of  three  distinct 
members  —  the  filament,  the  anther,  and  the  pollen, 
several  forms  of  which  may  be  seen  in  the  annexed 
engraving.  The  filament  is  the  stalk;  the  anther  is 


the  head,  and  the  pollen  is  the  dust  discharged  from 
the  anther.  The  pollen  is  the  matter  which  contains 
the  fructifying  principle.  The  mixture  of  this  with  the 
stigma,  where  the  seeds  are  formed,  is  necessary  to 
endow  them  with  the  principle  of  vegetable  life.  The 
granules  of  the  pollen  are  of  various  forms  ;  under  the 
microscope,  they  appear  to  be  globular,  oval,  square, 
and  of  various  other  shapes. 

The  disk,  or  hectarium,  is  placed  near  the  base  of  the 
stamens,  and  is  of  various  forms.  The  pistillum  occu- 
pies the  centre  of  the  flower,  and  is  the  female  or  re- 


productive  part  of  the   plant,  consisting  of  three  divis- 
ions—  the  seed-vessel  at  the  bottom;  the  style  at  the 


top;  and  the  stigma  between  the  two.  These  are 
usually  placed  below  the  anthers,  to  receive  the  pollen. 
The  Linnsean  system  of  classification,  as  before 
stated,  is  founded  upon  the  number,  connection,  and  sit- 
uation, of  the  sexual  organs  of  plants  —  the  stamens 
and  pistils.  It  was  intended  to  comprehend  the  whole 
vegetable  kingdom,  which  was  arranged  in  two  grand 
divisions,  —  namely,  plants  having  visible  flowers, 
(phono gamia,)  and  plants  having  no  visible  flowers, 
(cryptogamia.)  The  whole  are  included  in  twenty- 
four  classes ;  and  these  classes  are  subdivided  into 
orders,  genera,  and  species.  The  terms  used  to 
express  the  classes  are  compounded  of  the  Greek  nu- 
merals and  the  word  andria,  signifying  man.  These 
classes  are  subdivided  into  orders,  which  are  designated 
from  their  number  of  pistils  by  Greek  numerals  also, 
with  the  addition  of  the  word  gynia,  which  signifies 
woman.  The  following  is  a  summary  of  the  distin- 
guishing traits  of  the  respective  classes  :  — 

1.  Monandria,  with  one  stamen  —  Marestail. 

2.  Diandria,  with  two  stamens  —  Speedwell. 

3.  Triandria,  with  three  stamens  —  Grasses. 


4.  Tctramdria,  with  four  stamens— Bed-straw. 

5.  PaUmdrioj  with  five  stamens — Primrose. 

6.  Hexmdria,  with  six  stamens  —  Snowdrop. 

7.  Hfptmdria,  with  seven  stamens — Water-plan- 
tain. 

8.  OetaxdruL,  with  eight  stamens — Heath. 

9.  EiuuaMdria,    with   nine    stamens  —  Flowering- 
rash. 

10.  Dccojw/rto,  with  ten  stamens— Pink. 

11.  Dodecandriaj  with  eleven  to  nineteen  stamens 
—Agrimony. 

12.  Icosandria,  twenty  or  more,  inserted  into  the 
calyx— Rose. 

13.  Polyandria,  twenty  or  more,  inserted  into  the 
receptacle  —  Poppy. 

14.  Didynamia,  two  long  and  two  short  —  Foxglove, 

15.  Tetradynamia,  four  long  and  two  short  —  Wall- 
flower. 

16.  Monaddpkia,  filaments  combined  in  one  set  — 
Geranium. 

17.  Diadtlphia,  filaments  united  into  two  sets  — 
Pea. 

18.  PolyadtJpkia,  filaments  united  into  more  than 
two  sets  —  SL  John's  Wort. 

19.  Syngatesia,  anthers  united  into  a  tube,  flowers 
compound  — Thistle. 

20.  Gynandria,  stamens  situated  upon  the  style, 
above  the  gerraen  —  Orchis. 

21.  JfbwBria,  stamens  and  pistils  in  diflerent  flowers 
on  the  same  plant  —  Spurge. 

22.  DuBcio,  stamens  and  pistils  in  separate  flowers 
and  on  different  plants— Willow. 

v        xnt— 29 


338  BOTANY. 

23.  Polygamia,  stamens  and  pistils,  united  or  sep- 
arate, on  the  same  or  on  different  plants,  and  having 
two  different  kinds  of  perianth  —  Orache. 

24.  Cryptogamia,  stamen  and  pistils  not  visible  — 
Moss. 

The  preceding  classes  are  arranged  according  to  the 
number  of  stamens.  The  orders  are  twenty-six  in 
number,  arranged  according  to  the  number  of  the 
pistils  of  the  flowers. 


ZOOLOGY. 


HAVING  given  a  sketch  of  the  mineral  and  vegetable 
kingdoms,  we  now  come  to  ZOOLOGY,  which  is  the  sci- 
ence of  the  animal  kingdom,  and  embraces  the  natural 
history  of  those  beings  which  lice,  move,  and  feel  — 
from  man,  the  head  of  creation,  to  the  coralline  and  the 
sponge.  It  includes  alike  the  elephant  and  the  whale, 
with  the  minute  animalcules  of  which  a  thousand  may 
live  in  a  drop  of  water,  or  ten  thousand  in  the  stalk  of 
a  common  plant  Of  this  great  and  interesting  subject, 
we  can  give  but  a  brief  outline.* 

All  natural  objects  with  which  we  are  acquainted  by 
means  of  our  senses,  are  separated  into  two  great  divis- 
ions—  namely,  the  organic  and  the  inorganic.  These 
are  distinguished  by  their  laws,  which  draw  a  decided 
line  between  them,  and  the  boundaries  of  which  are 
therefore  sufficiently  defined.  The  organic  division 
comprehends  all  bodies  endued  with  vitality,  or  pos- 
sessing the  principle  of  life,  and  therefore  includes 
animals  and  plants ;  the  inorganic  embraces  all  those 
objects  which  are  destitute  of  life,  and  of  course  com- 
prehends the  mineral  kingdom. 

The  phenomena  manifested  by  all  organic  bodies  are 
the  results  of  an  inherent  power,  which  is  generally 

*  For  a  further  account  of  animals,  see  the  "  World  and  its 
Inhabitants,"  and  "  Anecdotes  of  Animals." 


termed  vital  principle  —  a  power,  the  essence  of  which 
is  enveloped  in  mystery,  and  upon  which  science  sheds 
no  light.  The  general  results  of  this  power  may  be 
said  to  consist  in  a  series  of  internal  movements  or 
actions,  having  no  relation  to  the  laws  of  chemistry  or 
mechanics,  and  which,  enduring  for  a  certain  definite 
period,  produces  those  external  characters  by  which 
we  at  once  know  an  organized  being ;  namely,  its 
shape  and  structure,  its  growth  by  the  absorption  and 
conversion,  into  a  part  of  itself,  of  extraneous  matter, 
and  its  power  of  resisting,  during  an  appointed  time, 
the  influence  of  external  agents. 

Hence  organic  bodies  seem  to  maintain  a  constant 
struggle  with  the  elements  around  them,  perpetually 
resisting  and  making  good  the  losses  which  their  ac- 
tions and  influences  occasion  ;  perpetually  throwing  off 
those  particles  which  are  no  longer  fit  for  the  keeping 
up  of  the  body's  integrity,  and  taking  up  others,  which 
they  mysteriously  convert  into  a  portion  of  them- 
selves—  thus  constantly  laboring  till  death. 

Inorganic  matter  does  not  increase  by  powers  within 
itself,  or  resist  external  agents  by  the  operations  of  a 
vital  principle.  Its  laws  are  those  only  of  mechanics, 
chemistry,  and  electricity. 

Organic  bodies,  therefore,  include  animals  and  plants. 
Such  is  the  resemblance  between  some  plants  and  the 
lowest  grades  of  animals,  that  certain  naturalists  main- 
tain that  the  two  kingdoms  run  one  into  the  other,  and 
that  there  is  no  defined  boundary  between  them.  It  is 
said  that  some  plants  appear  to  possess  feeling,  as  there 
are  species  which  shrink  from  the  touch ;  and  that 
others  display  intelligence  —  as,  for  instance,  a  potato, 


ZOOLOGY.  341 

growing  in  a  cellar,  will  wind  around  a  barrel,  or  other 
obstructing  object,  and  reach  forward  toward  a  window, 
to  obtain  light  and  air.  While  we  admit  the  truth  of 
these  facts,  we  may  still  doubt  the  inference.  Because 
we  cannot  see  the  point  of  division,  we  must  not  con- 
clude that  it  does  not  exist,  particularly  when  a  large 
survey  of  the  subject  seems  to  suggest  a  plain  design, 
on  the  part  of  the  Creator,  to  separate  them.  The 
following  are  some  of  the  characteristic  distinctions 
between  the  vegetable  and  animal  kingdoms  :  — 

The  power  of  voluntary  motion,  which  animals  in 
the  aggregate  possess,  demands  an  adaptation  of  the 
organs  of  nutrition,  and  hence  is  derived  their  first  and 
leading  character,  namely,  an  internal  apparatus  for 
the  reception  of  food,  in  which  it  undergoes  certain 
changes  before  its  admission  into  the  system  ;  an  ad- 
mission effected  by  a  multitude  of  minute  tubes  or 
vessels,  all  originating  within  this  apparatus.  Plants 
are  rooted  to  one  spot ;  they  cannot  employ  voluntary 
motion  in  the  search,  or  reception,  of  food  ;  they  have 
no  internal  digestive  apparatus,  and  the  absorbing 
tubes  of  nutriment  all  arise  from  the  external  surface. 
The  aliment  taken  in  by  animals  has  to  undergo  vari- 
ous operations  before  it  forms  a  juice  proper  for  ab- 
sorption ;  but  the  atmosphere  and  the  earth  present,  to 
vegetables,  juices  already  prepared,  and  which  may  be 
absorbed  immediately. 

Animal  bodies,  as  they  have  functions  more  numer- 
ous and  varied  than  plants,  possess,  with  a  structure 
accordingly  more  complicated,  a  circulatory  system, 
comprehending  the  arteries  and  veins,  by  which  their 
fluids  are  diffused  —  not,  as  is  the  case  with  plants,  by 
29* 


342  ZOOLOGY. 

the  influence  of  heat  and  atmospheric  action,  but  by 
internal  innate  energies. 

Animals  differ  from  plants  in  the  chemical  analysis 
of  their  constituent  principles.  The  essential  elements 
of  organized  matter  appear  to  be  carbon,  oxygen,  hy- 
drogen, azote  or  nitrogen,  together  with  alkaline  and 
earthy  salts:  now,  the  solid  parts  of  all  plants  contain 
carbon,  oxygen,  and  hydrogen,  but  no  azote.  The  solid 
parts  of  animals  consist  principally  of  lime  or  magnesia, 
united  with  carbonic  or  phosphoric  acids ;  and  in  those 
beings,  of  both  kingdoms,  which  appear  to  be  destitute 
of  solid  parts,  the  difference  is  even  still  more  wide  ; 
the  gum  or  mucilage  of  soft  plants  exhibiting  no  trace 
of  azote,  which  enters  as  a  constituent  into  the  gelatine 
or  albumen  of  soft  animals. 

Atmospheric  air  and  water  are  the  two  sources 
whence  the  plant  derives  the  principles  necessary  for 
the  maintenance  of  vitality.  Water  is  composed  of 
oxygen  and  hydrogen  ;  air,  of  oxygen,  azote,  and  car- 
bonic acid,  which  is  a  combination  of  oxygen  and 
carbon. 

Now,  of  these  elements,  the  vegetable  retains,  as 
essential  to  its  composition,  the  carbon,  the  hydrogen, 
and  part  of  the  oxygen  ;  and  exhales  or  throws  out  the 
azote  and  superfluous  volume  of  oxygen.  The  essen- 
tial function,  indeed,  of  vegetable  life  seems  to  be  the 
exhalation  of  oxygen  —  an  operation  requiring  the 
presence  of  that  universal  stimulus  of  nature,  light. 

The  principles  of  vegetable  composition,  —  namely, 
carbon  and  hydrogen  —  enter  also,  as  a  source  of  medi- 
ate or  immediate  nutriment,  into  the  composition  of 
animal  bodies.  But  the  constitution  of  animals  de- 


ZOOLOGY.  343 

mands  that  a  great  portion  of  this  hydrogen  and  carbon 
should  be  disposed  of  from  time  to  time,  and  that  azote 
should  be  absorbed.  This  operation  is  effected  through 
the  medium  of  the  atmosphere,  the  oxygen  of  which, 
combining  with  the  carbon  and  hydrogen  of  the  blood, 
is  exhaled  with  them  in  the  form  of  carbonic  acid  and 
water,  the  azote  appearing  to  remain. 

Plants  and  animals  may  thus  be  said  to  become 
mutual  sources  for  the  production  of  the  elements  each 
requires.  The  relations  they  bear  to  the  atmosphere 
are  inverse.  The  former  demands  water  and  carbonic 
acid,  and  the  latter  produce  it :  animals  demand  oxygen, 
and  the  vegetable  creation  is  perpetually  exhaling  it. 

Having  thus  separated  the  animal  from  the  vegetable 
kingdom,  we  have  only  space  to  qxhibit  the  general 
divisions  under  which  scientific  men  have  arranged 
all  that  has  a  claim  to  animal  existence,  with  a  few 
general  observations  upon  the  great  classes  of  the 
animal  kingdom. 

The  woods  and  fields  resound  on  every  side  with 
the  cries  and  voices  of  creatures  varying  in  form  and 
nature  ;  the  air  is  peopled  with  busy  tribes,  that  wan- 
der through  its  boundless  regions ;  the  wing  of  the 
bird  rustles  as  it  passes  us,  and  myriads  of  insects  are 
dancing  in  the  sun ;  the  waters  teem  with  life  ;  the 
ocean,  the  mighty  ocean,  is  replete  ;  even  the  "  drop 
upon  the  bucket "  is  a  lake  to  multitudes  of  animalcules, 
that  rejoice  and  multiply  in  its  mimic  floods,  or  pine  and 
die  as  it  evaporates.  We  cannot  pluck  a  leaf  from  a 
tree,  and  examine  it,  but  we  discover  it  to  be  a  little 
world,  peopled  with  pygmy  inhabitants,  that  play  their 
part  in  the  balance  of  creation — a  part  which  may, 


344  ZOOLOGY. 

indeed,  escape  the  researches  of  the  philosopher, 
but  which  infinite  wisdom  has  appointed.  Diversified, 
however,  and  multitudinous  as  they  are,  they  admit 
of  arrangements  or  classifications  which  unravel  the 
intricacy  of  the  subject,  and  divest  the  study  of  its  ap- 
parent difficulties.  It  was  a  want  of  this  system  which 
has  rendered  the  works  of  the  ancients,  on  natural 
objects,  little  more  than  records  of  disjointed  facts  or 
opinions,  without  mutual  bearing,  or  order,  or  plan, 
and  without  a  definite  end.  Hence  the  little  compara- 
tive progress  in  the  natural  sciences,  and  the  mistakes 
and  absurdities  which  we  find  to  have  prevailed  among 
nations  the  most  civilized  and  refined.  Modern  science 
received  a  new  impetus  from  the  writings  of  Bacon, 
Ray,  and  Linnaeus,  which  has  regulated  inquiry,  and 
produced  method  and  order.  Among  the  philosophers 
of  modern  times,  Cuvier  is  preeminent,  and  his  general 
outline  is  that  which  is  now  most  commonly  received. 
He  divides  the  animal  kingdom  into  four  grand  di- 
visions, namely, — 

1.  ANIMALIA    VERTEBRATA.  —  Vertebrate   animals, 
having  a  brain  enclosed  in  an  osseous   covering,  or 
skull,  and  a  vertebral  column,  —  as  quadrupeds,  birds, 
reptiles,  and  fishes. 

2.  ANIMALIA  MOLLTTSCA. — Molluscous  animals,  with- 
out any  internal  skeleton,  but  whose  muscles  are  at- 
tached to  a  soft  skin,  often  enclosed  in  a  hard  case, 
or  shell  of  lime,  as  oysters,  clams,  &c. 

3.  ANIMALIA  ARTICULATA.  —  Articulated  animals,  in 
which  the  body  is  divided  by  transverse  folds  into  a 
certain  number  of  rings ;  the  integuments  are  some- 
times hard,  sometimes  soft ;  but  the  muscles  are  always 


ZOOLOGY.  345 

attached  to  the  interior ;  the  trunk  is  often  furnished 
with  many  limbs,  consisting  of  numerous  joints,  but  is 
often  also  deficient  —  such  as  insects;  crustaceous  ani- 
mals, as  lobsters,  &c. 

4.  ANIMALIA  RADIATA. — Radiated  animals,  or  zoo- 
phytes, in  which  the  organs  of  movement  are  not 
disposed  symmetrically  on  each  side,  but  consist  of  an 
uneven  number,  disposed  like  rays  round  a  centre,  an 
instance  of  which  is  furnished  in  the  five-fingered  Jack ; 
they  possess  no  nervous  system,  nor  particular  organs 
of  sense  —  barely  traces  of  a  circulation ;  and  ap- 
proach in  their  structure  the  character  of  plants. 

VERTEBRATA. 

Vertebrate  animals  are  distinguished  by  an  internal 
bony  framework,  or  skeleton,  which  affords  solidity 
and  support.  Their  body  is  composed  of  a  head, 
trunk,  and  limbs :  the  head  consists  of  the  skull,  which 
encloses  and  protects  the  brain  ;  and  of  the  face,  which 
embraces  the  organs  of  taste,  smell,  sight,  and  hearing : 
the  head  rests  upon,  or  is  attached  to,  the  vertebral 
column,  which  is  composed  of  a  number  of  bones 
movable  one  on  another,  and  forming  altogether  a 
nanal  for  the  medulla  oblongata,  or  spinal  marrow. 
The  limbs  never  exceed  four,  and  are  in  pairs ;  but 
sometimes  one  pair  is  wanting,  sometimes  both.  The 
blood  is  always  red. 

This  great  family  is  divided  into  four  classes :  — 

1.  Mammalia,  or  mammiferous  animals,  including 
man,  and  most  quadrupeds. 

2.  Aves,  or  Birds. 


346  ZOOLOGY. 

3.  Reptilia,  or  Reptiles. 

4.  Pisces,  or  Fishes. 

The  mammiferous  animals  are  those  which  suckle 
their  young.  They  are  placed  in  the  first  class,  as 
being  the  most  perfectly  organized,  possessing  the 
most  acute  senses,  and  the  highest  degree  of  intelli- 
gence. This  class  contains  the  following  orders  :  — 

1.  Bimana,  man,  only  one  species. 

2.  Quadrumana,  four-handed  animals,  as  monkeys, 
apes,  and  baboons,  of  which  there  are  more  than  a 
hundred  species. 

3.  Carnivores,  or  Carnaria,  butchering  animals,  in- 
cluding bats,  bears,  weasels,  the  wolf,  dog,  fox,  hyena, 
lion,  tiger,  and  the  rest  of  the  cat  family. 

4.  Amphibia,  the  seal  kind,  including  the  walrus,  &c. 

5.  Marsupialia,  or  pouched  animals,  including  the 
opossum,  kangaroo,  &c. 

6.  Rodentia,  or  gnawing  animals,  as  squirrels,  rats, 
mice,  beavers,  rabbits,  &c. 

7.  Edentata,  without  front  teeth,  as  the  sloth,  arma- 
dillo, ant-eater. 

8.  Pachydermata,  thick-skinned  animals,  including 
the   elephant,   rhinoceros,  hippopotamus,  hog,  horse, 
camel,  giraffe,  lama,  deer,  goat,  sheep,  and  ox. 

9.  Cetacea,  the  whale  kind. 

All  the  mammalia  have  a  double  heart,  with  two 
ventricles  for  propelling  the  blood  ;  one  systematic,  or 
propelling  it  over  the  whole  body,  and  the  other  pul- 
monic,  or  sending  it  to  the  lungs ;  and  they  have  also 
two  auricles  as  appendages  to  the  heart  —  one  for  re- 
ceiving the  blood  from  the  lungs,  and  transmitting  it  to 


ZOOLOGY.  347 

the  systematic  ventricle ;  and  the  other  for  receiving 
the  blood  from  the  system  generally,  and  transmitting 
it  to  the  pulmonic  ventricle. 

The  b'.ood  of  all  is  red  and  warm,  but  differs  in  its 
temperature  in  different  species.  It  is  aerated  wholly 
in  the  lungs,  and  not  partially  by  air-cells  or  the  coats 
of  the  arteries,  as  in  birds ;  and  it  is  more  minutely 
distributed  over  the  system  than  in  any  other  class  of 
animals.  They  have  also  the  nervous  system — upon 
which,  as  we  usually  suppose,  sensation  and  apimaj 
intelligence  more  immediately  depend —  much  more  de- 
veloped than  any  other  animals ;  and  therefore,  though 
there  are  great  differences  among  them,  they  are, 
taken  all  together,  much  more  intelligent,  docile,  and 
capable  of  training,  than  any  of  the  other  classes  of 
animals. 

They  are  also  the  animals  which  are  most  useful  to 
man ;  and,  if  the  expression  may  be  allowed,  they  are 
most  kindred  to  him.  They  bear  a  part  with  him  ia 
his  labor,  their  flesh  supplies  him  with  his  best  food, 
and  their  covering  furnishes  him  with  his  warmest  and 
most  wholesome  clothing.  They  also  show  attach- 
ments to  man  which  are  not  shown  by  any  other 
animals ;  and  many  of  them  have  their  affection  un- 
shaken bv  even  very  severe  chastisement 

Mammalia  are  also  more  easily  studied  than  any  of 
the  other  classes  of  animals.  They,  generally  speak- 
ing, are,  with  ourselves,  inhabitants  of  the  surface  of 
the  earth;  for  though  a  few  live  habitually  in  the 
water,  a  few  others  under  ground,  and  a  few  others, 
still,  make  their  way  through  the  air  by  means  of  flying 
membranes,  yet  the  characteristic  locality  of  the  whole 


348  ZOOLOGY 

mammalia  is  the  surface  of  the  ground.  Generally 
speaking,  too,  they  do  not  retreat  into  holes  and  hiding- 
places,  as  is  the  case  with  most  ground  animals  of 
other  orders ;  they  come  out  openly,  and,  in  the  ma- 
jority of  instances,  to  the  day,  so  that  their  manners 
are  much  more  easily  studied  than  those  of  any  other 
animals. 

The  mammalia  have,  accordingly,  attracted  the  at- 
tention of  mankind  in  all  ages.  We  find  some  of  the 
most  beautiful  allusions  to  their  habits  in  the  writings 
of  the  prophets  and  poets  of  the  Jews,  which  leave  not 
the  least  doubt  that,  whether  they  had  a  regular  system 
of  the  natural  history  of  mammalia  or  not,  they  were 
well  acquainted  with  the  nature  of  the  animals. 

It  is  impossible,  in  the  compass  of  the  present  volume, 
to  enter  into  particular  descriptions  of  the  various  spe- 
cies which  belong  to  this  interesting  class  of  the  animal 
kingdom.  It  may  be  proper,  however,  to  say  some- 
thing of  him,  of  whom  it  is  written,  "  And  God  said, 
Let  us  make  man  in  our  own  image,  after  our  own  like- 
ness."— "  So  God  created  man  in  his  own  image,  in 
the  image  of  God  created  he  him  ;  male  and  female 
created  he  them." 

Of  man,  there  is  but  one  species,  and  one  genus. 
Confining  our  attention  to  him  in  a  merely  physical 
point  of  view,  he  is  the  most  perfect  of  all  terrestrial 
beings ;  not,  indeed,  in  size  or  animal  strength,  for  in 
these  qualities  many  excel  him,  but  in  the  refined,  the 
exalted  plan  and  model  upon  which  he  is  constructed. 
The  eagle,  it  is  true,  may  have  a  more  powerful 
vision;  the  hare  be  more  alive  to  every  sound;  the 
wild  dog  or  vulture  may  catch  the  faintest  scent  upon 


ZOOLOGY.  349 

the  gale ;  but  in  man  there  is  a  nice  balance,  an  ad- 
justment, a  felicitous  accuracy  of  the  senses,  which 
thus  expressly  tend  to  his  elevation  and  happiness, 
and,  at  the  same  time  that  they  minister  to  his  pleasure, 
enable  him  to  obtain  an  intimate  and  minute  acquaint- 
ance with  the  properties  of  the  w-srld  around  him. 
Hence  the  voice  of  melody ;  the  colors  of  earth  and 
sky ;  the  odors  of  spring ;  the  fruits  of  summer ;  the 
glorious  sun,  and  the  spangled  canopy  of  heaven,  are 
sources  of  gratification  and  delight  to  him.  Language, 
in  which  he  can  convey  his  wants,  his  desires,  and  the 
most  abstract  ideas  of  his  mind,  is  his  alone ;  and  his 
alone  are  reason  and  an  immortal  soul. 

While,  however,  on  the  topic  of  man's  physical  su- 
periority, we  cannot  omit  noticing  a  few  circumstances, 
because  peculiar  to  man,  at  once  proclaiming  his  own 
dignity  and  his  separation  from  inferior  creatures ;  we 
mean  his  attitude,  the  freedom  and  exquisite  mechanism 
of  his  hands,  and  his  natural  deficiency  in  weapons  of 
aggression  or  defence. 

With  the  attitude  of  man  we  naturally  associate 
ideas  of  exaltation  ;  and  this  attitude  is,  in  truth,  con- 
nected with  his  moral  greatness;  no  quadruped  ap- 
proaches him  in  volume  or  extent  of  brain ;  and  the 
blood  necessary  for  an  organ  so  developed  is  carried 
to  it  by  arteries,  which  do  not  subdivide,  as  in  most 
quadrupeds,  but  allow  that  full  and  free  circulation  its 
energies  require;  hence  a  horizontal  position  would 
induce  a  perpetual  liability  to  apoplexy,  and  render 
every  bodily  or  mental  exertion  a  hazardous  experi- 
ment. 

Man  —  sustaining  himself  on  his  feet  alone — pw»- 
xra. — 30 


350  ZOOLOGY. 

serves  the  entire  liberty  of  his  hands ;  and  the  situation 
of  these  organs  is  that  which  is  best  calculated  to  render 
them  available  and  useful.  But,  great  as  are  the  advan- 
tages derived  from  their  liberty,  more  are  attributable 
to  their  structure.  The  human  hand  is  strong  and 
powerful,  but,  at  the  same  time,  exquisitely  susceptible 
of  impressions,  and  gifted  with  the  most  delicate  tact 
Every  finger,  except  that  called  the  ring  Jinger,  is  ca- 
pable of  independent  movements  —  a  power  possessed 
by  no  other  animal ;  and  the  thumb  is  so  elongated  as 
to  meet  readily  the  tips  of  any  of  the  fingers :  the 
fingers  themselves,  and  especially  the  pulpy  tips  at 
their  extremities,  are  freely  supplied  by  a  nervous 
tissue,  which  communicates  a  discriminating  sensibility 
peculiar  to  our  race.  Hence  the  admirable  fitness  of 
the  hand  for  the  apprehension  and  examination  of  the 
minutest  objects,  and  the  precision  with  which  its  ac- 
tions are  executed. 

Man  possesses  neither  offensive  nor  defensive  weap- 
ons ;  but  this  very  deficiency  adds  to  his  improvement, 
inasmuch  as  it  throws  him  back  upon  his  internal 
resources,  and  calls  forth  the  energies  of  his  mind. 
His  first  step  in  civilization  is  to  clear  out  a  spot  of 
ground  for  his  dwelling ;  resist  the  inroads  of  the  wild 
and  ferocious  animals ;  drive  to  a  distance  or  extermi- 
nate the  intractable  ;  and  subdue  the  more  docile  to  him- 
self. Art  supplies  the  means  which  nature  has  with- 
held ;  and  the  rude  hunter  of  the  forest  founds  an 
abode,  and  rears  a  family,  to  be  the  forefathers  of  a 
mighty  nation. 

Multiplying  after  the  deluge,  the  human  race  has 
spread  itself  over  every  portion  of  the  globe,  and 


ZOOLOGY.  351 

ramified  into  a  thousand  tongues  and  nations.  Capable 
of  inhabiting  every  climate,  and  in  every  situation  sur- 
rounding himself  with  the  necessaries  of  life,  man 
peoples  the  burning  regions  of  the  torrid  zone,  and 
the  ice-girt  shores  of  the  Arctic  Ocean.  To  him  the 
mountain,  the  valley,  the  morass,  and  the  desert,  are 
alike  ;  and,  modifying  his  food  according  to  locality, 
he  thrives  upon  rice,  and  the  plantain,  and  the  palm-nut, 
on  the  plains  of  India  ;  upon  the  raw  flesh  and  blubber  of 
the  seal,  on  the  frozen  snows  of  Greenland.  Between 
these  points  there  are  innumerable  grades  and  distinc- 
tions in  habits,  in  manners,  in  food,  in  civilization,  and 
moral  qualities ;  but,  different  as  the  tribes  into  which 
the  human  race  is  divided  may  appear,  they  may  be 
ultimately  reduced  to  about  five  standing  varieties,  the 
descendants  of  a  common  parent.  These  have  been 
characterized  as  the  Caucasian,  which  includes  the 
nations  of  Europe,  and  such  in  ancient  times  as  have 
been  most  distinguished  for  civilization  and  power ;  the 
Mongolian,  to  which  are  referred  the  mighty  empires 
of  China  and  Japan  ;  the  Ethiopian,  occupying  the 
interior  of  Africa ;  the  American ;  and  the  Malay, 
which  includes  the  natives  of  the  peninsula  of  Malacca, 
of  Borneo,  Java,  the  isles  of  the  Indian  Ocean,  Aus- 
tralia, and  the  islands  of  the  Pacific. 

It  were  useless  to  inquire,  and  impossible  to  give  any 
satisfactory  solution,  or  theory,  upon  which  to  account 
for  the  hereditary  characteristics  which  attach  to  these 
different  varieties  of  mankind  :  climate,  food,  modes 
of  life  in  remote  ages,  a  primeval  peculiarity  in  the 
early  progenitors,  which  has  continued  itself  to  their 
latest  descendants,  or  causes  now  unknown,  may  have 


352  ZOOLOGY. 

all,  in  their  turn,  contributed  to  the  diversity  that  exists. 
One  feature,  however,  which  pervades  human  nature 
through  all  its  varieties,  in  every  age,  in  every  nation, 
proclaims  a  common  origin.  History,  however  re- 
motely we  trace  its  records,  whether  sacred  or  profane, 
discovers  this  trait  in  every  page,  and  our  own  expe- 
rience has  made  us  acquainted  with  it :  we  mean  the 
universal  degeneracy  of  the  human  race  —  a  fact  which, 
however  men  may  have  differed  as  to  its  cause,  has 
in  every 'generation  been  acknowledged;  and,  as  if 
the  memory  of  Eden  still  lingered  on  the  earth,  has 
been  blended  with  a  looking-back  to  a  traditionary 
period  of  innocence  and  purity  before  "  all  flesh  had 
corrupted  his  way ; "  and  the  sage  and  the  poet  have 
alike  lamented  the  long-passed  golden  age. 

The  class  Aves  furnishes,  in  the  admirable  adapta- 
tion of  structure  to  the  modes  of  life  in  the  several 
species,  a  most  interesting  theme  of  inquiry ;  that  of 
the  Reptilia  abounds  in  various  and  wonderful  phenom- 
ena ;  and  the  Pisces,  inhabitants  of  the  world  of  waters, 
may  well  excite  our  admiration  by  their  variety  and 
their  peculiar  endowments. 

Nor  are  the  invertebrate  animals  without  their  claims 
to  our  attention ;  but  our  limited  space  compels  us, 
reluctantly,  to  deny  them  a  particular  description. 


ADVERTISEMENT-CABINET  LIBRARY. 

PARLEY'S  CABINET  LIBRARY, 

For  Schools  and  Families. 

THIS  work  consists  of  Twenty  Volumes,  and  contains 
^fjine  hundred  different  subjects,  and  is  illustrated  by  fae 
hundred  Engravings. 

O"  It  is  an  entirely  original  series,  recently  written  and 
completed  by  S.  G.  GOODRICH,  the  author  of  Peter  Parley'a 
Tales. 

[D=  This  is  the  only  library  that  has  been  expressly  written 
for  a  School  and  Family  Library.  It  is  adopted  into  many  of 
the  libraries  of  the  leading  schools  and  seminaries  in  New 
England  and  New  York,  and  has  been  introduced,  in  the 
space  of  a  few  months,  into  more  than  three  thousand  fami- 
lies, in  Boston,  New  York,  and  Philadelphia. 

The  following  is  a  list  of  the  Volumes,  each  containing 
about  320  pages,  16mo. :  — 

BIOGRAPHICAL  DEPARTMENT. 

Vol  1.  —  LIVES  OF  FAMOUS  MEN  OF  MODERN  TIMES. 
"  2. —  Livts  OF  FAMOUS  MEN  OF  ANCIENT  TIMES. 
««  3.  —  CURIOSITIES  OF  HUMAN  NATURE  ;  OR,  TH E  LIVES 

OF  ECCENTRIC  AND  WONDERFUL  PERSONS. 
"     4  —LIVES   OF    BENEFACTORS;    INCLUDING  PATRIOTS, 

INVENTORS,   DISCOVERERS,  &c. 
««     5.  —  LIVES  OF  FAMOUS  AMERICAN  INDIANS. 
**    6.  —  LIVES  OF  CELEBRATED  WOMEN. 

HISTORICAL  DEPARTMENT. 

**     7.  —  LIGHTS  AND  SHADOWS  OF  AMERICAN  HISTORT. 
"     8.  —  LIGHTS  AND  SHADOWS  or  EUROPEAN  HISTORT. 
««     9. —  LIGHTS  AND  SHADOWS  OF  ASIATIC   HISTORT. 
•«  10. —  LIGHTS  AND  SHADOWS  OF  AFRICAN  HISTORT. 

"  11. HlSTORV  OF  THE  AMERICAN  l.NDIANS. 

««  12.  —  MANNERS,  CUSTOMS,  AND  ANTIQUITIES    or    TH« 
AMERICAN  INDIANS. 

MISCELLANEOUS. 

««  13.  — A  GLANCE  AT  THE  SCIENCES,  ASTRONOMT,  NATO- 

RAL  PHILOSOPHY, &c. 
«*  14.  —  WONDERS  OF  GEOLOGY. 
**  15.  —  ANECDOTES  OF  THE  ANIMAL  KINGDOM. 
"  16.  —  A   GLANCE   AT    PHILOSOPHY,   MENTAL,   MORAL, 

AND  SOCIAL. 
•«  17. —  BooK  OF  LITERATURE,  ANCIENT   AND    MODERN, 

WITH  SPECIMENS. 


.ADVERTISEMENT— CABINET  LIBRARY. 

Vol.18.  —  ENTERPRISE,  INDUSTRY,  AND  ART  OF  MAN. 

"  19.  —  MANNERS  AND  CUSTOMS  OF  ALL  NATIONS. 

"  20.  — THE  WORLD  AND  ITS  INHABITANTS. 

10°  These  works  are  designed  to  exhibit,  in  a  popular 
form,  SELECT  BIOGRAPHIES,  ANCIENT  AND  MODERN;  the 
Wonders  and  Curiosities  of  HISTORY,  NATURE,  ART,  SCI- 
ENCE, AND  PHILOSOPHY,  with  the  Practical  Duties  of  Life. 

It  cannot  be  deemed  invidious  to  say,  that  no  similar  work 
has  met  with  equal  favor  at  the  hands  of  the  public,  as  the 
following  testimonials,  among  many  others,  will  show  :  — 
Tlit  Hon.  H.  O.  Otis,  of  Boston,  says, 

I  view  Has  the  best  compendium  of  useful  learning  and  information,  re- 
specting its  proposed  contents,  fur  the  use  of  young  persons  and  schools, 
that  has  fallen  within  my  knowledge.  It  abounds  in  illustrations  of  the 
history  of  the  world,  and  the  customs  and  manners  of  nations,  that  may  be 
read  by  general  scholars  of  any  age,  with  pleasure. 
The  Rev.  Dr.  Sprague  says,  Albany, 

1  regard  the  Cabinet  Library  as  a  most  important  accession  to  the  means 
of  intellectual  and  moral  culture,  especially  in  respect  to  the  rising  genera- 
tion. But  while  it  is  peculiarly  adapted  to  the  young,  it  may  be  read  by 
persons  of  any  age  with  both  pleasure  and  profit.  To  men  of  business,  who 
have  not  leisure  to  read  extensively,  and  indeed  to  all  who  would  keep  up 
with  the  times,  the  work  is  invaluable.  It  is  also  suited  to  the  various 
members  of  the  family  circle,  £5-  and  is  among-  the  very  be.it  of  the  libraries 
for  public  schools.  1  learn  that  it  is  introduced  into  the  public  schools  of 
tins  i  ity,  (Albany,)  and  various  other  places,  and  I  cannot  doubt  that  it 
will  ultimately  be  adopted  in  our  seminaries  of  learning  generally. 
Charles  Sprague,  Esq.,  of  Boston,  says, 

I  have  read,  with  both  pleasure  and  profit,  all  the  numbers  of  your  very 
Instructive  Cabinet  Library.  My  friend  and  namesake,  the  Rev.  Dr.  Sprague, 
has  so  exactly  expressed  my  opinion  of  the  work,  that  I  need  only  adopt 
his  language,  in  recommending;  it,  as  I  cheerfully  do,  to  the  favorable 
attention  of  both  teachers  and  learners. 

From  the  Quincy  Patriot, 

We  recommend  it  (Parley's  Cabinet  Library)  as  peculiarly  valuable  to 
families.  We  often  see  one  young  man  taking  precedence  of  others  in  the 
race  of  life.  If  we  could  read  his  history  minutely,  we  should  see  the 
explanation  of  the  case  to  be,  that  he  had  a  better  head  or  a  better  heart 
than  others.  Now  we  know  of  no  works  so  well  calculated  to  mould  the 
head  and  heart  aright  as  those  of  "  Peter  Parley." 

Those  parents  who  wish  to  have  their  children  "  go  ahead  "  in  life, 
should  place  Parley's  Cabinet  Library  within  their  reach.  We  have  never 
seen  a  work  better  suited  to  bestow  instruction,  or  that  inculcates  truth  in 
•  more  pleasant  fashion. 

From  the  Boston  Courier, 

They  are  exceedingly  agreeable  books,  and  such  as  young  and  old  may 
peruse  with  pleasure  and  profit.  The  moral  and  religious  account  to  which 
the  author  turns  every  subject  must  render  the  work  peculiarly  suitable 
to  the  family  and  the  school  library.  We  cheerfully  commend  the  work 
to  the  public  as  one  of  sterling  value. 

From  the  Boston  Mas, 

It  is  a  compact  family  and  school  library  of  substantial  reading,  which  If 
delightful  in  point  of  style,  and  wholesomeln  its  moral,  social,  an 
tendency 


ADVERTISEMENT-CABINET  UBBAXfST. 

From  the  Baton  Post, 

We  hardly  know  when  we  have  been  better  pleased  with  a  publica- 
tion than  this. 

From  HUM' i  Merchant's  Magazine, 

This  work,  now  complete,  is  the  most  elaborate  of  the  works  of  the  au- 
thor for  the  young  ;  and  we  think  it  quite  the  best.  It  is  a  lihrary  of  facts. 
and  seems  intended  to  cultivate  a  taste  fur  this  kind  of  reading.  It  is  said 
that  "truth  is  stranger  than  fiction,"  and  no  one  who  has  perused  these 
pages  can  feel  any  necessity  for  seeking  excitement  in  the  high-wrought 
pages  of  romance.  Every  subject  touched  by  the  author  seems  invested 
with  a  lively  interest;  and  even  dry  statistics  are  made,  like  steel  be- 
neath the  strokes  of  the  flint,  to  yield  sparks  calculated  to  kindle  the  mind. 
In  treating  of  the  iron  manufacture,  —  a  rather  hard  subject,  it  would  seem, 
—  we  are  told  that,  every  "  working  day,  fifty  millions  of  nails  are  made, 
bought,  sold,  and  used  in  the  United  states  ;  "  and,  in  speaking  of  the  man- 
ufacture of  cotton,  we  are  informed  that  the  Merrimack  mills  of  Lowell 
alone  "  spin  a  thread  of  sufficient  length  to  belt  the  world,  at  the  equator, 
in  two  hours." 

The  work  was  doubtless  intended  for  the  young  ;  and  we  think  it  quite 
equal,  for  this  object,  to  any  thiug  that  has  been  produced  ;  yet  it  is  also 
suited  to  the  perusal  of  all  classes,  especially  to  men  of  business,  who  find 
little  leisure  for  reading,  and  who  yet  are  unwilling  to  be  left  behind  in 
the  great  march  of  knowledge  and  improvement.  As  there  it  nine  a  strong  de- 
tire,  especially  among  the  enlightened  friends  of  education  in  this  state,  to  hate 
tie  common  schools  supplied  with  suitable  books  far  libraries,  ve  heartily  com- 
mfiut  this  series  to  tht  notice  of  all  teho  are  desirous  of  obtaining  books  for 
this  object.  They  are  unquestionably  among  the  best  that  hate  been  prepared 
for  school  libraries,  being  every  way  attractive  and  instructive. 

Xo  one  can  fail  to  be  pleased  with  the  simplicity  and  elegance  of  the 
style,  and  with  the  vein  of  cheerfulness,  humanity,  and  morality,  which 
runs  through  the  pages  of  the  volumes.  The  moral  influence  of  the  work, 
especially  upon  the  young,  cannot  fail  to  be  in  the  highest  degree  effective 
and  salutary. 

From  the  Troy  Whig, 

They  are  written  in  an  easy  and  graceful  style,  and  are  compiled  trom 
the  most  authentic  sources.    They  will  be  found  highly  attractive  to  young 
people  of  both  sexes,  and  worthy  to  be  read  by  persons  of  mature  age. 
From  the  Albany  Advertiser. 

It  would  be  difficult  to  find  any  where,  in  such  convenient  compass, 
•o  much  healthy  and  palatable  food  for  the  youthful  mind  as  u  furnished 
by  Parley's  Cabinet  Library. 

From  the  Albany  Argus. 

We  know  of  no  series  of  volumes  on  kindred  subjects  so  good  as  thew 
for  parents  to  put  into  the  hands  of  their  children.  It  is  due  not  only  to 
the  author,  who  has  rendered  great  service  to  the  cause  of  American  lit- 
erature, but  to  the  work  itself,  ant!  to  the  best  interests  of  the  youth  cf  our 
nation,  that  these  volumes  should  be  scattered  all  over  the  land. 
From  the  .Yew  England  Puritan. 

We  cordially  recommend  the  work  to  the  perusal  of  all. 
From  the  Boston  Post, 

The  rery  best  vork  of  its  class  is  Parley's  Cabinet  Library.  It  combines 
•  vast  deal  of  useful  information,  conveyed  in  an  exceedingly  interesting 
style.  The  beauty  of  the  typographical  execution,  the  cheapness  of  the 
volumes,  and  the  great  intrinsic  merit  of  their  contents,  must  render  the 
work  one  of  general  popularity. 

From  the  Boston  Courier, 

As  we  have  quoted  so  Largely  from  Mr.  Goodrich's  work,  we  ought  to 
wy-  what  it  richly  merits  —  that  it  is  a  pleasing  and  useful  sr-je*,  and 


ADVERTISEMENT-CABINET  LIBRARY. 

that  it  is  calculated  not  only  tu  instruct  and  amuse,  but  to  cultivate  virtu 
oils  and  patriotic  sentiments.  With  those  who  read  for  mere  amusement, 
it  is  worthy  of  attention,  for  the  author  has  ingeniously  contrived  to  giv* 
truth  all  the  charms  of  fiction. 

From  the  Albany  Advertiser. 

It  ought  to  be,  and  no  doubt  will  be,  extensively  introduced  into  schools 
From  Vie  Bay  State  Democrat, 

The  volumes  are  illustrated  with  spirited  wood  engravings,  and  printed 
In  Dickinson's  neatest  style.  Altogether,  they  present  decidedly  the  nio.st 
attractive  appearance  as  to  matter  and  form,  of  any  works  we  have  seen  for 
a  long  time. 

From  the  Quiney  Aurora. 

Parley's  Cabinet  Library  is  a  publication  of  rare  excellence.  No  writei 
of  the  present  day  invests  the  themes  of  which  he  treats  with  livelier  inter- 
est than  the  well-known  Peter  Parley.  His  pen  imparts  to  history  and  biog- 
raphy the  charm  of  romance  ;  while,  at  the  same  time,  it  unfolds  rich  and 
enduring  treasures  of  practical  and  useful  knowledge. 

The  animal,  the  mineral,  and  vegetable  kingdoms  of  nature  present, 
beneath  his  pencil,  the  attractions  of  a  grand  museum.  The  publication 
of  his  Cabinet  Library  will  accomplish  much,  in  our  opinion,  to  eradicate 
the  eagerness  for  fiction  which  engrosses  so  extensively  the  public  mind. 
The  perusal  of  these  volumes  will  convince  the  reader  that  reality  has 
charms  as  potent,  and  far  more  satisfying  than  those  of  the  ideal  world. 
We  know  of  no  work, comprehended  within  equal  limits,  capable  of  atlbrd- 
ing  richer  intellectual  banqueting. 

From  the  Boston  Traveller. 

We  deem  it  but  a  discharge  of  our  duty  to  our  readers,  to  urge  this  val- 
uable series  upon  their  attention.     The  whole  series  will  cost  but  a  trifle, 
yet  they  may  and  doubtless  will  be  the  deciding  means  of  insuring  suc- 
cess in  life  to  many  a  youth  who  shall  enjoy  the  means  of  reading  them. 
From  the  Boston  Recorder. 

They  are  written  in  a  pleasing  style,  and  are  enlivened  by  numerous 
characteristic  anecdotes.     The  series  will  form  a  very  valuable  library. 
From  the  Boston  Post, 

It  is  an  admirable  publication  for  the  family  and  school  library.  Its  top- 
KS  are  interesting  and  important,  and  presented  in  a  simple  but  effective 
atyle. 

From  the  Boston  Atlas, 

Parley's  Cabinet  Library  is  worthy  of  all  encouragement.  It  is  elienp 
not  only  in  promise,  but  in' fact.  It  is  also  calculated  to  exercise  a  whole- 
some influence.  Like  every  thing  from  the  same  author,  it  stronaly  in- 
culcatcs  virtue  and  religion,  and  at  the  same  time  it  arrays  truth  in  a  miise 
so  comely  and  attractive,  that  it  is  likely  to  win  many  votaries  of  fiction 
to  companionship  with  it.  There  is  great  need  of  such  works  at  this  time 

City  of  Rochester,  Sept.  2.     '       j 

Whereas,  the  Board  of  Education  have  examined  a  series  of  books 
called  "  Parley's  Cabinet  Library,"  now  in  course  of  publication  by  Samue! 
G.  Goodrich,  Esq.,  (the  celebrated  Peter  Parley,)  embracing,  in  the  cours4 
of  twenty  volumes,  the  various  subjects  of  history,  biography,  geography, 
the  manners  and  customs  of  different  nations,  the  condition  of  the  arts, 
sciences,  &.c. ;  and  whereas,  this  Board  are  satisfied  that  the  same  are  high- 
ly useful  to  the  young  :  therefore, 

Resolved,  that  we  recommend  that  the  same  be  procured  by  trustees  for 
'he  several  school  libraries,  at  the  earliest  practicable  period.  A  true  copy 
<the  minutes,  I.  F.  MACF,  Sup'L 


This  book  is  DUE  on  the  last 
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